(E)-5-hydroxy-7-methoxy-3-(2'-hydroxybenzyl)-4-chromanone isolated from Portulaca oleracea L. suppresses LPS-induced inflammation in RAW 264.7 macrophages by downregulating inflammatory factors.

CONTEXT: Portulaca oleracea L. is herbaceous succulent annual plant, which belongs to the Portulacaceae family. Many studies have shown its wide spectrum of pharmacological activities such as anti-cancer and anti-diabetic effects. OBJECTIVES: The objective of this study was to identify the anti-inflammatory effects of HM-chromanone isolated from Portulaca oleracea L. in LPS-stimulated RAW 264.7 macrophages. MATERIALS AND METHODS: LPS (1 µg/ml)-stimulated mouse RAW 264.7 macrophages were used to assess the anti-inflammatory effect of HM-chromanone (10-50 µM). Cell viability was evaluated by MTT assay. In addition, the production of intracellular ROS, superoxide anion, lipid peroxide, NO, and PGE2, and activity of antioxidant enzymes were analyzed. The expressions of iNOS, COX-2, IκB, NF-κB, TNF-α, IL-1ß and IL-6 were evaluated by western blot analysis. RESULTS: HM-chromanone has demonstrated that there is no significant cytotoxic effect on the viability of RAW 264.7 macrophages. In LPS-stimulated RAW 264.7 cells, HM-chromanone treatment was found to significantly inhibit the production of intracellular ROS, superoxide anion and lipid peroxide, while enhancing the activity of antioxidant enzymes such as SOD, catalase, and GSH-px. Additionally, HM-chromanone treatment was observed to inhibit NO and PGE2 production by inhibiting the expression of iNOS and COX-2. Subsequently, HM-chromanone was observed to significantly suppress LPS-induced expression of IκB, NF-κB, TNF-α, IL-1ß and IL-6. DISCUSSION AND CONCLUSION: Overall, our results suggested that HM-chromanone suppresses LPS-induced inflammation in RAW 264.7 macrophages by downregulating the expression of inflammatory factors.

Pheophorbide A from Gelidium amansii improves postprandial hyperglycemia in diabetic mice through α-glucosidase inhibition.

This study was designed to determine the inhibitory effects of pheophorbide A on carbohydrate digesting enzymes and its ability to improve postprandial hyperglycemia in streptozotocin (STZ)-induced diabetic mice. Pheophorbide A caused noticeable inhibitory effects on α-glucosidase and α-amylase, with half-maximal inhibitory concentrations (IC50 ) of 80.65 ± 5.90 and 76.48 ± 6.31 µM, respectively. The pheophorbide-mediated inhibition of α-glucosidase and α-amylase was significantly more effective than that of the positive control, acarbose. The increase in postprandial blood glucose levels was more significantly suppressed in the pheophorbide A group than in the control group of STZ-induced diabetic mice. In addition, the area under the curve was decreased by pheophorbide A intake in STZ-induced diabetic mice. Our results suggested that pheophorbide A may help to improve postprandial hyperglycemia by inhibiting the activity of carbohydrate digesting enzymes.

Cyanidin-3-rutinoside protects INS-1 pancreatic ß cells against high glucose-induced glucotoxicity by apoptosis.

Exposure to high levels of glucose may cause glucotoxicity, leading to pancreatic ß cell dysfunction, including cell apoptosis and impaired glucose-stimulated insulin secretion. The aim of this study was to explore the effect of cyanidin-3-rutinoside (C3R), a derivative of anthocyanin, on glucotoxicity-induced apoptosis in INS-1 pancreatic ß cells. Glucose (30 mM) treatment induced INS-1 pancreatic ß cell death, but glucotoxicity and apoptosis significantly decreased in cells treated with 50 µM C3R compared to that observed in 30 mM glucose-treated cells. Furthermore, hyperglycemia increased intracellular reactive oxygen species (ROS), lipid peroxidation, and nitric oxide (NO) levels, while C3R treatment reduced these in a dose-dependent manner. C3R also increased the activity of antioxidant enzymes, markedly reduced the expression of pro-apoptotic proteins (such as Bax, cytochrome c, caspase 9 and caspase 3), and increased the expression of the anti-apoptotic protein, Bcl-2, in hyperglycemia-exposed cells. Finally, cell death was examined using annexin V/propidium iodide staining, which revealed that C3R significantly reduced high glucose-induced apoptosis. In conclusion, C3R may have therapeutic effects against hyperglycemia-induced ß cell damage in diabetes.

A phlorotannin constituent of Ecklonia cava alleviates postprandial hyperglycemia in diabetic mice.

CONTEXT: 2,7″-Phloroglucinol-6,6'-bieckol is a type of phlorotannin isolated from brown algae, Ecklonia cava Kjellman (Phaeophyceae; Laminareaceae). 2,7″-Phloroglucinol-6,6'-bieckol mediates antioxidant activities. However, there has been no research on improving postprandial hyperglycaemia using 2,7″-phloroglucinol-6,6'-bieckol. OBJECTIVE: This study investigated the inhibitory effects of 2,7″-phloroglucinol-6,6'-bieckol on activities of α-glucosidase and α-amylase as well as its alleviating effect on postprandial hyperglycaemia in streptozotocin-induced diabetic mice. MATERIALS AND METHODS: α-Glucosidase and α-amylase inhibitory assays were carried out. The effect of 2,7″-phloroglucinol-6,6'-bieckol on hyperglycaemia after a meal was measured by postprandial blood glucose in streptozotocin-induced diabetic and normal mice. The mice were treated orally with soluble starch (2 g/kg BW) alone (control) or with 2,7″-phloroglucinol-6,6'-bieckol (10 mg/kg bw) or acarbose (10 mg/kg BW) dissolved in 0.2 mL water. Blood samples were taken from tail veins at 0, 30, 60, and 120 min and blood glucose was measured by a glucometer. RESULTS: 2,7″-Phloroglucinol-6,6'-bieckol showed higher inhibitory activities than acarbose, a positive control against α-glucosidase and α-amylase. The IC50 values of 2,7″-phloroglucinol-6,6'-bieckol against α-glucosidase and α-amylase were 23.35 and 6.94 µM, respectively, which was found more effective than observed with acarbose (α-glucosidase IC50 of 130.04 µM; α-amylase IC50 of 165.12 µM). In normal mice, 2,7″-phloroglucinol-6,6'-bieckol significantly suppressed the postprandial hyperglycaemia caused by starch. The 2,7″-phloroglucinol-6,6'-bieckol administration group (2349.3 mmol·min/L) had a lower area under the curve (AUC) glucose response than the control group (2690.83 mmol·min/L) in diabetic mice. DISCUSSION AND CONCLUSION: 2,7″-Phloroglucinol-6,6'-bieckol might be used as an inhibitor of α-glucosidase and α-amylase as well as to delay absorption of dietary carbohydrates.

The protective effect of daidzein on high glucose-induced oxidative stress in human umbilical vein endothelial cells.

Endothelial cell dysfunction is considered a major cause of vascular complications in diabetes. In the present study, we investigated the protective effect of daidzein, a natural isoflavonoid, against high-glucose-induced oxidative damage in human umbilical vein endothelial cells (HUVECs). Treatment with a high concentration of glucose (30 mM) induced oxidative stress in the endothelial cells, against which daidzein protected the cells as demonstrated by significantly increased cell viability. In addition, lipid peroxidation, intracellular reactive oxygen species (ROS) generation, and indirect nitric oxide levels induced by the high glucose treatment were significantly reduced in the presence of daidzein (0.02-0.1 mM) in a dose-dependent manner. High glucose levels induced the overexpression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and NF-κB proteins in HUVECs, which was suppressed by treatment with 0.04 mM daidzein. These findings indicate the potential of daidzein to reduce high glucose-induced oxidative stress.

Jicama (Pachyrhizus erosus) extract increases insulin sensitivity and regulates hepatic glucose in C57BL/Ksj-db/db mice.

This study investigated the effect of jicama extract on hyperglycemia and insulin sensitivity in an animal model of type 2 diabetes. Male C57BL/Ksj-db/db mice were divided into groups subsequently fed a regular diet (controls), or diet supplemented with jicama extract, and rosiglitazone. After 6 weeks, blood levels of glucose and glycosylated hemoglobin were significantly lower in animals administered the jicama extract than the control group. Additionally, glucose and insulin tolerance tests showed that jicama extract increased insulin sensitivity. The homeostatic index of insulin resistance was lower in the jicama extract-treated group than in the diabetic control group. Administration of jicama extract significantly enhanced the expressions of the phosphorylated AMP-activated protein kinase and Akt substrate of 160 kDa, and plasma membrane glucose transporter type 4 in skeletal muscle. Jicama extract administration also decreased the expressions of glucose 6-phosphatase and phosphoenol pyruvate carboxykinase in the liver. Jicama extract may increases insulin sensitivity and inhibites the gluconeogenesis in the liver.

Phloroglucinol Protects INS-1 Pancreatic ß-cells Against Glucotoxicity-Induced Apoptosis.

Decreasing numbers, and impaired function, of pancreatic ß-cells are key factors in the development of type 2 diabetes. This study was designed to investigate whether phloroglucinol protected pancreatic ß-cells against glucotoxicity-induced apoptosis using a rat insulinoma cell line (INS-1). High glucose treatment (30 mM) induced INS-1 cell death; however, the level of glucose-induced apoptosis was significantly reduced in cells treated with 100-µM phloroglucinol. Treatment with 10-100-µM phloroglucinol increased cell viability and decreased intracellular levels of reactive oxygen species, nitric oxide, and lipid peroxidation dose-dependently in INS-1 cells pretreated with high glucose. Furthermore, phloroglucinol treatment markedly reduced the protein expression of Bax, cytochrome c, and caspase 9, while increasing anti-apoptotic Bcl-2 protein expression. Cell death type was examined using annexin V/propidium iodide staining, revealing that phloroglucinol markedly reduced high glucose-induced apoptosis. These results demonstrated that phloroglucinol could be useful as a potential therapeutic agent for the protection of pancreatic ß-cells against glucose-induced apoptosis.

Improving the Effect of Ferulic Acid on Inflammation and Insulin Resistance by Regulating the JNK/ERK and NF-κB Pathways in TNF-α-Treated 3T3-L1 Adipocytes.

In this study, ferulic acid was investigated for its potential in suppressing TNF-α-treated inflammation and insulin resistance in adipocytes. Ferulic acid suppressed TNF-α, IL-6, IL-1ß, and MCP-1. TNF-α increased p-JNK and ERK1/2, but treatment with ferulic acid (1, 10, and 50 µM) decreased p-JNK and ERK1/2. TNF-α induced the activation of IKK, IκBα, and NF-κB p65 compared to the control, but ferulic acid inhibited the activation of IKK, IκBα, and NF-κB p65. Following treatment with TNF-α, pIRS-1ser307 increased and pIRS-1tyr612 decreased compared to the control. Conversely, as a result of treatment with 1, 10, and 50 µM ferulic acid, pIRS-1ser307 was suppressed, and pIRS-1tyr612 was increased. Therefore, ferulic acid reduced inflammatory cytokine secretion by regulating JNK, ERK, and NF-κB and improved insulin resistance by suppressing pIRS-1ser. These findings indicate that ferulic acid can improve inflammation and insulin resistance in adipocytes.

Effect of diphlorethohydroxycarmalol isolated from Ishige okamurae on apoptosis in 3 T3-L1 preadipocytes.

Obesity is an important issue in the world of public health and preventive medicine. Inhibition of proliferation of preadipocytes plays an important role in proposed antiobesity mechanisms. In this study, we investigated the effect of diphlorethohydroxycarmalol (DPHC) isolated from Ishige okamurae on the apoptotic pathway. The results showed that DPHC inhibited population growth in 3 T3-L1 preadipocytes as assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Flow cytometric analysis of 3 T3-L1 preadipocytes showed that the number of early and late apoptotic cells increases in a dose-dependent manner after exposure to DPHC, while the number of normal cells was reduced. Our findings indicate that the induction of apoptosis in 3 T3-L1 preadipocytes by DPHC is mediated through the activation of caspase-3, Bax, and caspase-9, and then through the cleavage of poly(ADP-ribose) polymerase and the down-regulation of Bcl-2. The data also indicated that treatment with DPHC inhibits histone deacetylase activity in 3 T3-L1 preadipocytes. These results show that DPHC efficiently induces apoptosis in 3 T3-L1 preadipocytes.

HM-chromanone isolated from Portulaca oleracea L. alleviates insulin resistance and inhibits gluconeogenesis by regulating palmitate-induced activation of ROS/JNK in HepG2 cells.

Oxidative stress is a major cause of hepatic insulin resistance. This study investigated whether (E)-5-hydroxy-7-methoxy-3-(2-hydroxybenzyl)-4-chromanone (HM-chromanone), a homoisoflavonoid compound isolated from Portulaca oleracea L., alleviates insulin resistance and inhibits gluconeogenesis by reducing palmitate (PA)-induced reactive oxygen species (ROS)/c-Jun NH2-terminal kinase (JNK) activation in HepG2 cells. PA treatment (0.5 mM) for 16 h resulted in the highest production of ROS and induced insulin resistance in HepG2 cells. HM-chromanone, like N-acetyl-1-cysteine, significantly decreased PA-induced ROS production in the cells. HM-chromanone also significantly inhibited PA-induced JNK activation, showing a significant reduction in tumor necrosis factor and interleukin expression levels. Thus, HM-chromanone decreased the phosphorylation of Ser307 in insulin receptor substrate 1, while increasing phosphorylation of serine-threonine kinase (AKT), thereby restoring the insulin signaling pathway impaired by PA. HM-chromanone also significantly increased the phosphorylation of forkhead box protein O, thereby inhibiting the expression of gluconeogenic enzymes and reducing glucose production in PA-treated HepG2 cells. HM-chromanone also increased glycogen synthesis by phosphorylating glycogen synthase kinase-3ß. Therefore, HM-chromanone may alleviate insulin resistance and inhibit gluconeogenesis by regulating PA-induced ROS/JNK activation in HepG2 cells.

Scopoletin protects INS-1 pancreatic ß cells from glucotoxicity by reducing oxidative stress and apoptosis.

This study investigated whether scopoletin could protect INS-1 pancreatic ß cells from apoptosis and oxidative stress caused by high glucose. Cells were pretreated with glucose (5.5 or 30 mM) and then treated with 0, 5, 10, 25, or 50 µM Scopoletin. Cell viability and insulin secretion were measured in addition to ROS, TBARS, NO and antioxidant enzymes. Western blot analysis and flow cytometric assessment of apoptosis were also carried out. High glucose of 30 mM caused glucotoxicity and cell death in INS-1 pancreatic ß cells. However, 5, 10, 25 or 50 µM scopoletin increased the level of cell viability as concentrations increased. The levels of ROS, TBARS, and NO increased by high glucose were significantly decreased after scopoletin treatment. Scopoletin also raised antioxidant enzyme activities up against oxidative stress produced by high glucose. These effects influenced the apoptosis pathway, raising levels of anti-apoptotic protein, Bcl-2, and reducing levels of pro-apoptotic proteins, including JNK, Bax, cytochrome C, and caspase 9. Annexin V/propidium staining indicated that scopoletin significantly lowered high glucose-produced apoptosis. These results indicate that scopoletin can protect INS-1 pancreatic ß cells from glucotoxicity caused by high glucose and have potential as a pharmaceutical material to protect the pancreatic ß cells.

HM-Chromanone Alleviates Hyperglycemia by Protecting Pancreatic Islet Cells in Streptozotocin-Induced Diabetic Mice.

We examined the effects of HM-chromanone (HMC) on alleviating hyperglycemia and protecting pancreatic ß-cells from streptozotocin (STZ)-induced damage in C57BL/6J mice. HMC was administered to STZ-induced diabetic mice at 10 or 30 mg/kg, for 14 days. Thereafter, changes in fasting blood glucose levels, insulin-secretion, histopathological examination of pancreas islet cell and apoptotic protein levels, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay were determined. The results revealed that HMC dose-dependently improved blood glucose concentrations and alleviated pancreatic islet cells damage. In diabetic mice, degeneration of the islet cells was observed wherein they appeared shrunken, with hyaline deterioration, nuclear dissolution, and condensation. However, morphology of the islet cell was restored, and nuclei were visibly rounded in the HMC (30 mg/kg)-administered diabetic mice. In addition, ß-cell numbers were markedly increased in HMC mice compared to STZ-induced diabetic mice, and the number of cells stained with glucagon was decreased. HMC markedly decreased the expression of proapoptotic proteins and increased antiapoptotic proteins, and the number of apoptotic cells detected by TUNEL was elevated. HMC decreased expression of interleukin (IL)-1ß, IL-6, and tumor necrosis factor-α in diabetic mice. Moreover, HMC increased antioxidant-enzymes activity, and decreased reactive oxygen species generation. In conclusion, the results demonstrate the potential of HMC to alleviate hyperglycemia by protecting the pancreatic ß-cells in diabetic mice.

HM-chromanone from Portulaca oleracea L. inhibits protein tyrosine phosphatase 1B and mitigates glucose production in insulin-resistant HepG2 cells.

This study aimed to identify the effect of (E)-5-hydroxy-7-methoxy-3-(2'-hydroxybenzyl)-4-chromanone (HM-chromanone), isolated from Portulaca oleracea L., on tyrosine phosphatase 1B (PTP1B) and glucose production in insulin-resistant HepG2 cells. The results revealed that HM-chromanone significantly decreases PTP1B expression and glucose production in insulin-resistant HepG2 cells. Furthermore, a molecular docking stimulation showed HM-chromanone inhibits PTP1B by binding to its active site. Additionally, HM-chromanone was found to significantly modulate insulin receptor substrate-1 (IRS1) by decreasing phosphorylated serine 307 and increasing phosphorylated tyrosine 612 and activating phosphatidylinositol 3-kinase (PI3K) in insulin-resistant HepG2 cells. Furthermore, HM-chromanone augmented the phosphorylation of Akt and forkhead box protein O1 in insulin-resistant HepG2 cells in a dose-dependent manner at the concentrations of 15-60 µM. Additionally, it significantly reduced the expression of glucose 6-phosphatase and phosphoenolpyruvate carboxykinase, which are main enzymes included in hepatic gluconeogenesis. Consequently, HM-chromanone was confirmed to significantly decrease glucose production and increase glucose uptake in insulin-resistant HepG2 cells.

HMC Ameliorates Hyperglycemia via Acting PI3K/AKT Pathway and Improving FOXO1 Pathway in ob/ob Mice.

Type 2 diabetes is a disease characterized by hyperglycemia and is a growing health problem worldwide. Since many known diabetes drugs are side effects, it is necessary to develop natural substances with guaranteed safety. HM-chromanone isolated from Portulaca oleracea L. is a homoisoflavonoid compound. We investigated the effects of HM-chromanone on hyperglycemia and its mechanism in C57BL/6J ob/ob mice. C57BL/6J-Jms Slc mice were used as the control group, and C57BL/6J-ob/ob mice were divided into three groups: ob/ob (control), metformin (Met; positive control), and HM-chromanone (HMC). Fasting blood glucose was lower in the HMC group than those in the ob/ob group. Insulin resistance was improved by reducing HbA1c, plasma insulin, and HOMA-IR levels in the HMC group. HMC administration decreased the phosphorylation of IRS-1ser307 and increased the phosphorylation of IRS-1tyr612, PI3K, phosphorylation of AKTser473, and PM-GLUT4 in the skeletal muscles of ob/ob mice, indicating improved insulin signaling. HMC administration also increased the phosphorylation of FOXO1 in the liver of ob/ob mice. This inhibited PEPCK and G6pase involved in gluconeogenesis and regulated phosphorylation of glycogen synthase kinase 3ß and glycogen synthase involved in glycogen synthesis. In conclusion, HM-chromanone ameliorates hyperglycemia by PI3K/AKT and improves the FOXO1 in ob/ob mice.

Dieckol isolated from Ecklonia cava protects against high-glucose induced damage to rat insulinoma cells by reducing oxidative stress and apoptosis.

Pancreatic ß cells are very sensitive to oxidative stress and this might play an important role in ß cell death with diabetes. The protective effect of dieckol, one of the phlorotannin polyphenol compounds purified from Ecklonia cava (E. cava), against high glucose-induced oxidative stress was investigated by using rat insulinoma cells. A high-glucose (30 mM) treatment induced the death of rat insulinoma cells, but dieckol, at a concentration 17.5 or 70 µM, significantly inhibited the high-glucose induced glucotoxicity. Treatment with dieckol also dose-dependently reduced thiobarbituric acid reactive substances (TBARS), the generation of intracellular reactive oxygen species (ROS), and the nitric oxide level increased by a high glucose concentration. In addition, the dieckol treatment increased the activities of antioxidative enzymes including catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-px) in high glucose-pretreated rat insulinoma cells. Dieckol protected rat insulinoma cells damage under high glucose conditions. These effects were mediated by suppressing apoptosis and were associated with increased anti-apoptotic Bcl-2 expression, and reduced pro-apoptotic cleaved caspase-3 expression. These findings indicate that dieckol might be useful as a potential pharmaceutical agent to protect against the glucotoxicity caused by hyperglycemia-induced oxidative stress associated with diabetes.

HM-chromanone suppresses hepatic glucose production via activation of AMP-activated protein kinase in HepG2 cell.

We investigated whether (E)-5-hydroxy-7-methoxy-3-(2-hydroxybenzyl)-4-chromanone (HM-chromanone) could suppress the transcription factors expression and enzymes involved in glucose production by activating AMPK in hepatocytes. HepG2 cells were treated with a medium containing HM-chromanone (5-100 µM), compound C (10 µM) and insulin (100 nM). Glucose production and glycogen synthesis assay were determined using a glucose assay kit and glycogen assay kit, respectively. Activities of AMP-activated protein kinase (AMPK), acetyl CoA carboxylase (ACC), cAMP response element-binding protein (CREB), PPAR coactivator-1α (PGC1α), CREB-regulated transcription coactivator 2 (CRTC2), Glycogen synthase kinase (GSK3ß), Phosphoenolpyruvate carboxykinase (PEPCK), glycogen synthase (GS), Glucose 6-phosphatase (G6pase) and ß-actin were determined by Western blot analysis. HM-chromanone significantly inhibited hepatic glucose production and increased glycogen synthesis by activating glycogen synthase. HM-chromanone induced the phosphorylation of CRTC2 and GSK-3ß by phosphorylating AMPK in HepG2 cells, which was confirmed by compound C. Furthermore, it significantly decreased the phosphorylation of CREB in a time- and concentration-dependent manner, and the effect was reversed in the presence of compound C. Therefore, the complex formation of CRTC2 and CREB was inhibited. HM-chromanone inhibited the expression of PGC-1α, PEPCK, and G6Pase genes involved in production of hepatic glucose. The results showed that HM-chromanone activates AMPK in a time and concentration dependent manner, thus suppressing hepatic glucose production and increasing glycogen synthesis in HepG2 cells.

A bioactive component of Portulaca Oleracea L., HM-chromanone, improves palmitate-induced insulin resistance by inhibiting mTOR/S6K1 through activation of the AMPK pathway in L6 skeletal muscle cells.

Increased free fatty acid levels in the blood are common in obesity and cause insulin resistance associated with type 2 diabetes in the muscles. Previous studies have confirmed the antidiabetic and anti-obesity potential of (E)-5-hydroxy-7-methoxy-3-(2-hydroxybenzyl)-4-chromanone (HM-chromanone). However, it is unknown how HM-chromanone alleviates obesity-related insulin resistance in L6 skeletal muscle cells. Palmitate induced insulin resistance and reduced glucose uptake, whereas HM-chromanone significantly increased glucose uptake. In palmitate-treated L6 skeletal muscle cells, HM-chromanone stimulated liver kinase B1 (LKB1) and 5'-adenosine monophosphate-activated protein kinase (AMPK) phosphorylation. The AMPK inhibitor compound C, and the LKB1 inhibitor radicicol blocked the effects of HM-chromanone. Furthermore, HM-chromanone significantly inhibited mammalian target of rapamycin (mTOR) and ribosomal protein S6 kinase 1 (S6K1) activation, but there was no change in protein kinase C θ (PKC θ) expression. When pAMPK was inhibited with compound C, the effect of HM-chromanone on the inhibition of mTOR and S6K1 was significantly diminished. This indicates that HM-chromanone inhibits mTOR and S6K1 activation through pAMPK activation. Inhibition of mTOR and S6K1 by HM-chromanone significantly reduced IRS-1Ser307 and IRS-1Ser632 phosphorylation, leading to insulin resistance. This resulted in an increase in PM-GLUT4 (glucose transporter 4) expression, thereby stimulating glucose uptake in insulin-resistant muscle cells. HM-chromanone can improve palmitate-induced insulin resistance by inhibiting mTOR and S6K1 through activation of the AMPK pathway in L6 skeletal muscle cells. These results show the therapeutic potential of HM-chromanone for improving insulin resistance in type 2 diabetes.

HM-chromanone reverses the blockade of insulin signaling induced by high glucose levels in human HepG2 cells.

This study investigated whether (E)-5-hydroxy-7-methoxy-3-(2'-hydroxybenzyl)-4-chromanone (HM-chromanone) could counteract the high glucose level-induced blockade of insulin signaling in human HepG2 cells. Cells were pre-incubated with glucose (5.5 or 33 mM) and then incubated with a medium containing various concentrations of HM-chromanone. Assays for glucose uptake, glycogen synthesis, and glucose production were performed. Western blotting helped elucidate the underlying molecular mechanisms. High glucose concentration (33 mM) significantly increased p-IRS-1ser307 levels and decreased p-Akt levels. However, HM-chromanone significantly decreased p-IRS-1ser307 levels while increasing p-IRS-1tyr612 and Akt levels, which restored insulin signaling disturbed by high glucose concentration. HM-chromanone significantly increased p-AMPK levels, which were reduced by high glucose in HepG2 cells. Knockdown of AMPK using siRNA increased p-IRS-1ser307 and decreased p-Akt levels, even after treatment with HM-chromanone in high glucose concentration-treated cells. HM-chromanone stimulated glycogen synthesis by increasing p-GSK3ßser9 and decreasing p-GSser641 levels in HepG2 cells under high glucose concentration; this effect was blocked by AMPK siRNA. HM-chromanone significantly decreased PEPCK, G6Pase, and hepatic glucose production, which were also blocked by AMPK siRNA. These results suggest that HM-chromanone could reverse insulin signaling blockade (induced by high glucose levels) through the activation of AMPK and stimulation of glucose uptake and glycogen synthesis in HepG2 cells.

HM-chromanone attenuates TNF-α-mediated inflammation and insulin resistance by controlling JNK activation and NF-κB pathway in 3T3-L1 adipocytes.

Obesity is a major public health problem worldwide and causes inflammation and insulin resistance in adipose tissue. We investigated the ability of (E)-5-hydroxy-7-methoxy-3-(2'-hydroxybenzyl)-4-chromanone (HM-chromanone) isolated from Portulaca oleracea to attenuate the activation of inflammatory cytokines and signaling pathways associated with tumor necrosis factor (TNF)-α-mediated inflammation and insulin resistance in 3T3-L1 adipocytes. TNF-α triggers the release of inflammatory cytokines and activation of the mitogen-activated protein kinase and nuclear factor (NF)-κB signaling pathways. In this study, HM-chromanone inhibited the production of inflammatory cytokines and chemokines [TNF-α, interleukin (IL)-6, IL-1ß, and monocyte chemoattractant protein 1] involved in inflammation and insulin resistance. Furthermore, TNF-α treatment increased c-Jun-NH2 terminal kinase (JNK) phosphorylation, whereas HM-chromanone significantly decreased JNK phosphorylation in a dose-dependent manner. TNF-α treatment increased the activation of inhibitor kappa B (IκB) kinase (IKK), IκBα, and NF-κBp65 compared with that of the control. However, HM-chromanone significantly blocked IKK, IκBα, and NF-κBp65 activation. Upon adipocyte stimulation with TNF-α, phosphorylated insulin receptor substrate (pIRS)-1 serine 307 levels increased and pIRS-1 tyrosine 612 levels decreased compared with those of the control. Upon treatment with HM-chromanone, serine 307 phosphorylation of IRS-1 was inhibited and tyrosine 612 phosphorylation of IRS-1 was increased. Thus, HM-chromanone improved TNF-α-mediated inflammation and insulin resistance by regulating JNK activation and the NF-κB pathway, thereby reducing inflammatory cytokine secretion and inhibiting serine phosphorylation of IRS-1 in the insulin signaling pathway. These results suggest the potential of HM-chromanone to improve inflammatory conditions and insulin resistance in adipocytes.

Pheophorbide A isolated from Gelidium amansii inhibits adipogenesis by regulating adipogenic transcription factors and AMPK in 3T3-L1 adipocytes.

Adipocyte lipid accumulation causes adipocyte hypertrophy and adipose tissue increment, leading to obesity. As part of our efforts to isolate antiobesity agents from natural products, we first isolated the active compound from the extract of Gelidium amansii through bioassay-guided fractionation. We then hypothesized that pheophorbide A isolated from G amansii inhibits adipogenesis by downregulating adipogenic transcription factors; therefore, the antiadipogenic effects of pheophorbide A were investigated in 3T3-L1 adipocytes. On differentiation of 3T3-L1 preadipocytes into adipocytes, they were treated with pheophorbide A (0-83 µM). Pheophorbide A inhibited triglyceride accumulation (half maximal inhibitory concentration = 114.2 µM) and stimulated glycerol release in a dose-dependent manner in 3T3-L1 adipocytes. In addition, pheophorbide A significantly decreased leptin concentrations in 3T3-L1 adipocytes. Pheophorbide A inhibited adipogenesis by suppressing the expression of adipogenic transcriptional factors including peroxisome proliferator-activated receptor γ, CCATT/enhancer binding protein α, sterol regulatory element binding protein 1c, and fatty acid synthase. It also induced the expression of phosphorylation of AMP-activated protein kinase. Therefore, these results suggest that pheophorbide A may be useful for preventing or treating obesity because of its inhibitory effect on adipogenesis.