Yohan Kim

Effect of eriodictyol on glucose uptake and insulin resistance in vitro.

Eriodictyol [2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-2,3-dihydrochromen-4-one] is a flavonoid with anti-inflammatory and antioxidant activities. Because inflammation and oxidative stress play critical roles in the pathogenesis of diabetes mellitus, the present study was designed to explore whether eriodictyol has therapeutic potential for the treatment of type 2 diabetes. The results show that eriodictyol increased insulin-stimulated glucose uptake in both human hepatocellular liver carcinoma cells (HepG2) and differentiated 3T3-L1 adipocytes under high-glucose conditions. Eriodictyol also up-regulated the mRNA expression of peroxisome proliferator-activated receptor γ2 (PPARγ2) and adipocyte-specific fatty acid-binding protein (aP2) as well as the protein levels of PPARγ2 in differentiated 3T3-L1 adipocytes. Furthermore, it reactivated Akt in HepG2 cells with high-glucose-induced insulin resistance. This response was strongly inhibited by pretreatment with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, indicating that eriodictyol increased Akt phosphorylation by activating the PI3K/Akt pathway. These results imply that eriodictyol can increase glucose uptake and improve insulin resistance, suggesting that it may possess antidiabetic properties.

(2S)-naringenin from Typha angustata inhibits vascular smooth muscle cell proliferation via a G0/G1 arrest.

ETHNOPHARMACOLOGICAL RELEVANCE Typha angustata is used in traditional Chinese medicine for a variety of clinical disorders. Its pharmacological actions include beneficial effects on hyperlipidemia and myocardial infarction, as well as labor-inducing and antibacterial effects. AIM OF THE STUDY We investigated the mechanism underlying the ability of (2S)-naringenin, an active compound from Typha angustata, to inhibit the proliferation of vascular smooth muscle cells (VSMCs). MATERIALS AND METHODS After measuring the antiproliferative effect of (2S)-naringenin on VSMC proliferation using cell proliferation and viability assays, the possible involvement of a signaling pathway associated with platelet-derived growth factor receptor β (PDGF-Rβ), extracellular signal regulated kinase 1/2 (ERK1/2), phosphatidylinositol 3-kinase (PI3K)-linked protein kinase B (Akt/PKB), or phospholipase C-γ1 (PLCγ1) was investigated by immunoblotting. Moreover, the effect of (2S)-naringenin on DNA synthesis and the cell cycle was examined using a [(3)H]-thymidine incorporation assay and flow cytometry. RESULTS (2S)-Naringenin significantly inhibited PDGF-BB-induced VSMC proliferation in a concentration-dependent manner, but did not affect signaling pathways associated with PDGF-Rβ, Akt/PKB, ERK1/2, or PLCγ1. However, (2S)-naringenin suppressed DNA synthesis via a G(0)/G(1) cell cycle arrest. Accordingly, the expression of cyclins D1 and E and cyclin-dependent kinases 2 and 4 was inhibited in a concentration-dependent manner; moreover, the phosphorylation of retinoblastoma protein was suppressed. CONCLUSIONS Our results show that (2S)-naringenin inhibited the PDGF-BB-induced proliferation of VSMCs via a G(0)/G(1) arrest; thus, (2S)-naringenin may be valuable as a therapeutic agent for managing atherosclerosis and/or vascular restenosis.

Stimulation of Glucose Uptake and Improvement of Insulin Resistance by Aromadendrin

Agents that stimulate glucose uptake and improve insulin resistance may be useful in the management of type 2 diabetes mellitus (DM). Thus, the aims of this study were to assess the effects of aromadendrin, a flavonoid from Gleditsia sinensis Lam., on stimulation of glucose uptake and improvement of insulin resistance and to characterize the molecular mechanisms underlying these activities. Insulin-stimulated glucose uptake was measured in HepG2 cells and in differentiated 3T3-L1 adipocytes using 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), a fluorescent D-glucose analog. Expression of the peroxisome proliferator-activated receptor-γ2 (PPARγ2) and adipocyte-specific fatty acid binding protein (aP2) mRNAs and the PPARγ2 protein was analyzed in adipocytes using RT-PCR and immunoblotting, respectively. Insulin-stimulated protein kinase B (Akt/PKB) phosphorylation was measured in high glucose-induced, insulin-resistant HepG2 cells. Similar to 30 µmol/l rosiglitazone, treatment with 30 µmol/l aromadendrin significantly stimulated insulin-sensitive glucose uptake in both HepG2 cells and 3T3-L1 adipocytes. Aromadendrin treatment also enhanced adipogenesis and caused increases in the expression of PPARγ2 and aP2 mRNAs and the PPARγ2 protein in differentiated 3T3-L1 adipocytes. In high glucose-induced, insulin-resistant HepG2 cells, aromadendrin reversed the inhibition of Akt/PKB phosphorylation in response to insulin, which could be abrogated by pretreatment with LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor. Aromadendrin treatment induced adipogenesis by increases in PPARγ2 expression, resulting in stimulation of glucose uptake and ameliorated insulin resistance. These findings suggest that aromadendrin may represent a potential therapeutic candidate for the management of type 2 DM.

Anti-proliferative actions of 2-decylamino-5,8-dimethoxy-1,4-naphthoquinone in vascular smooth muscle cells.

Naphthoquinone derivatives have been reported to possess various pharmacological activities, such as antiplatelet, anticancer, antifungal, and antiviral properties. In this study, we investigated the effects of a newly-synthesized naphthoquinone derivative, 2-decylamino-5,8-dimethoxy-1,4-naphthoquinone (2-decylamino-DMNQ), on VSMC proliferation and examined the molecular basis of the underlying mechanism. In a dose-dependent manner, 2-decylamino-DMNQ inhibited PDGF-stimulated VSMC proliferation with no apparent cytotoxic effect. While 2-decylamino-DMNQ did not affect PDGF-Rβ or Akt, it did inhibit the phosphorylation of Erk1/2 and PLCγ1 induced by PDGF. Moreover, 2-decylamino-DMNQ suppressed DNA synthesis through the arrest of cell cycle progression at the G(0)/G(1) phase, including the suppression of pRb phosphorylation and a decrease in PCNA expression, which was related to the downregulation of cell cycle regulatory factors, such as cyclin D1/E and CDK 2/4. It was demonstrated that both U0126, an Erk1/2 inhibitor, and U73122, a PLCγ inhibitor, increased the proportion of cells in the G(0)/G(1) phase of the cell cycle. Thus, these results suggest that 2-decylamino DMNQ has an inhibitory effect on PDGF-induced VSMC proliferation and the mechanism of this action is through cell cycle arrest at the G(0)/G(1) phase. This may be a useful tool for studying interventions for vascular restenosis in coronary revascularization procedures and stent implantation.

A new iridoid and effect on the rat aortic vascular smooth muscle cell proliferation of isolated compounds from Buddleja officinalis

A new iridoid, named methylscutelloside (1) together with 19 known compounds belonging to the iridoids (2-4), monoterpenoids (5), flavonoids (6-8), triterpenoids (9-14), and phenylethanoids (15-20) were isolated from the flowers of Buddleja officinalis. Their chemical structures were elucidated on the basis of physicochemical properties, and by spectroscopic methods including 1D, 2D NMR, and MS. All isolated compounds were tested in vitro for their effects on the proliferation of rat aortic vascular smooth muscle cells (VSMCs). Among them, iridoids were the main active components and showed significant inhibitory effects on PDGF-BB-induced proliferation in rat aortic VSMCs.

Enhanced effect of losartan and rosuvastatin on neointima hyperplasia

The beneficial effects of losartan and rosuvastatin on neointimal formation have been well characterized, but little is known about the combined treatment benefit of these two drugs. This study was designed to investigate the synergistic effect of losartan combined with rosuvastatin on the magnitude of protective action in vascular injury mediated by cuff-induced neointimal formation model in vivo. Losartan at 20 mg/kg or rosuvastatin at 40 mg/kg significantly decreased both the neointimal formation and BrdU-positive cells in neointima, indicating the inhibition of cell proliferation including a progress of DNA synthesis. The combination treatment used lower doses of losartan with rosuvastatin (10 + 20 & 5 + 10 mg/kg, respectively) that proved to be significant in decreasing the neointimal formation and BrdU incorporation. These results were comparable to the diminution attained with monotherapy of either drug in higher doses. Interaction index measured by isobolar method indicated drug synergism in these two combinations of both drugs at lower doses. Therefore, the administration of losartan and rosuvastatin in combination with low doses synergistically decreased in cuffinduced neointimal formation by reducing cell proliferation, suggesting that this drug synergism may be fully effective with, lower adverse effects, for the treatment of vascular remodeling such as restenosis.

Murrayafoline A Induces a G0/G1-Phase Arrest in Platelet-Derived Growth Factor-Stimulated Vascular Smooth Muscle Cells

The increased potential for vascular smooth muscle cell (VSMC) growth is a key abnormality in the development of atherosclerosis and post-angioplasty restenosis. Abnormally high activity of platelet-derived growth factor (PDGF) is believed to play a central role in the etiology of these pathophysiological situations. Here, we investigated the anti-proliferative effects and possible mechanism(s) of murrayafoline A, a carbazole alkaloid isolated from Glycosmis stenocarpa Guillamin (Rutaceae), on PDGF-BB-stimulated VSMCs. Murrayafoline A inhibited the PDGF-BB-stimulated proliferation of VSMCs in a concentration-dependent manner, as measured using a non-radioactive colorimetric WST-1 assay and direct cell counting. Furthermore, murrayafoline A suppressed the PDGF-BB-stimulated progression through G0/G1 to S phase of the cell cycle, as measured by [3H]-thymidine incorporation assay and cell cycle progression analysis. This anti-proliferative action of murrayafoline A, arresting cell cycle progression at G0/G1 phase in PDGF-BB-stimulated VSMCs, was mediated via down-regulation of the expression of cyclin D1, cyclin E, cyclin-dependent kinase (CDK)2, CDK4, and proliferating cell nuclear antigen (PCNA), and the phosphorylation of retinoblastoma protein (pRb). These results indicate that murrayafoline A may be useful in preventing the progression of vascular complications such as restenosis after percutaneous transluminal coronary angioplasty and atherosclerosis.

Inhibitory effect of a novel naphthoquinone derivative on proliferation of vascular smooth muscle cells through suppression of platelet-derived growth factor receptor β tyrosine kinase.

This study was designed to investigate the antiproliferative effect of a novel naphthoquinone derivative, 2-undecylsulfonyl-5,8-dimethoxy-1,4-naphthoquinone (2-undecylsulfonyl-DMNQ), on platelet-derived growth factor (PDGF)-stimulated vascular smooth muscle cells (VSMCs) and examine the possible molecular mechanism of its antiproliferative action. 2-Undecylsulfonyl-DMNQ significantly inhibited PDGF-stimulated cell number and DNA synthesis, and arrested the PDGF-stimulated progression through G0/G1 to S phase of cell cycle supported by the suppression of pRb phosphorylation and cyclin D1/E, CDK2/4 and PCNA expressions. 2-Undecylsulfonyl-DMNQ dose-dependently inhibited the PDGF-stimulated phosphorylation of phospholipase Cγ (PLCγ), protein kinase B (Akt/PKB), signal transducers and activators of transcription 3 (STAT3) and extracellular signal-regulated kinase 1/2 (ERK 1/2). In addition, 2-undecylsulfonyl-DMNQ inhibited PDGF-induced PDGF receptor β (PDGF-Rβ) dimerization and the phosphorylation of Tyr(579/581), Tyr(716), Tyr(751) and Tyr(1021) in PDGF-Rβ. However, 2-undecylsulfonyl-DMNQ has no antiproliferative effect on epidermal growth factor (EGF)- or fetal bovine serum (FBS)-stimulated VSMCs. In conclusion, these findings suggest that the antiproliferative effects of 2-undecylsulfonyl-DMNQ on PDGF-stimulated VSMCs are due to the blockade of receptor dimerization and autophosphorylation on specific tyrosine residues of PDGF-Rβ, which resulted in the subsequent suppression of signaling cascades and a cell cycle arrest. Our observation may explain an important mechanism to block the integration of multiple signals generated by growth factor receptor activation for prevention of VSMC proliferation in cardiovascular diseases.

5,8-Dimethoxy-2-Nonylamino-Naphthalene-1,4-Dione Inhibits Vascular Smooth Muscle Cell Proliferation by Blocking Autophosphorylation of PDGF-Receptor β

As the abnormal proliferation of vascular smooth muscle cells (VSMCs) plays a critical role in the development of atherosclerosis and vascular restenosis, a candidate drug with antiproliferative properties is needed. We investigated the antiproliferative action and underlying mechanism of a newly synthesized naphthoquinone derivative, 5,8-dimethoxy-2-nonylamino-naphthalene-1,4-dione (2-nonylamino-DMNQ), using VSMCs treated with platelet-derived growth factor (PDGF). 2-Nonylamino-DMNQ inhibited proliferation and cell number of VSMCs induced by PDGF, but not epidermal growth factor (EGF), in a concentration-dependent manner without any cytotoxicity. This derivative suppressed PDGF-induced [3H]-thymidine incorporation, cell cycle progression from G0/G1 to S phase, and the phosphorylation of phosphor-retinoblastoma protein (pRb) as well as the expression of cyclin E/D, cyclin-dependent kinase (CDK) 2/4, and proliferating cell nuclear antigen (PCNA). Importantly, 2-nonylamino-DMNQ inhibited the phosphorylation of PDGF receptorβ(PDGF-Rβ) enhanced by PDGF at Tyr579, Tyr716, Tyr751, and Tyr1021 residues. Subsequently, 2-nonylamino-DMNQ inhibited PDGF-induced phosphorylation of STAT3, ERK1/2, Akt, and PLCγ1. Therefore, our results indicate that 2-nonylamino-DMNQ inhibits PDGF-induced VSMC proliferation by blocking PDGF-Rβ autophosphorylation, and subsequently PDGF-Rβ-mediated downstream signaling pathways.

Synergistic improvement in insulin resistance with a combination of fenofibrate and rosiglitazone in obese type 2 diabetic mice

Peroxisome proliferator-activated receptor (PPAR) α, which is abundant in the liver, increases lipoprotein lipase activity, resulting in a decrease of triglyceride (TG) levels. PPARγ, which is abundant in adipose tissue, stimulates adipocyte differentiation and adipogenesis, and results in an increase in insulin sensitivity. Fenofibrate, a PPARα agonist, is commonly used to treat dyslipidemia, and rosiglitazone, a PPARγ agonist, is effective in improving glycemic control. To examine the synergistic effects of rosiglitazone in combination with fenofibrate, an obese type 2 diabetes mellitus (DM) mouse model was established by the combined administration of streptozotocin and nicotinamide and fed on a high-fat diet (35% of energy as fat) for 3 weeks. The mice had significantly higher plasma glucose concentrations and insulin resistance, as examined by an oral glucose tolerance test and insulin challenge test compared with normal mice. After establishing a dose-response curve for each drug, the drugs were orally administered for 3 weeks either alone or in combination. After individual administration of fenofibrate, HDL cholesterol levels significantly increased, and plasma glucose and TG levels decreased in obese type 2 DM mice. The individual administration of rosiglitazone showed increased insulin resistance (QUICKI). However, HDL cholesterol and TG levels were not significantly changed. In a combination of fenofibrate at 25 mg/kg and rosiglitazone at 1.25 mg/kg there was a decrease in plasma glucose and TG levels, and a combination of fenofibrate at 50 mg/kg and rosiglitazone at 2.5 mg/kg showed an increase in plasma HDL cholesterol levels. Moreover, parameters related to insulin resistance (HOMA-IR) and insulin sensitivity (QUICKI) were improved significantly. Thus, our results show that combination therapy with lower doses of fenofibrate and rosiglitazone ameliorates the type 2 DM condition to a greater extent than high doses of either individual monotherapy.