Nobiletin attenuates neurotoxic mitochondrial calcium overload through K+ influx and ΔΨm across mitochondrial inner membrane.

Mitochondrial calcium overload is a crucial event in determining the fate of neuronal cell survival and death, implicated in pathogenesis of neurodegenerative diseases. One of the driving forces of calcium influx into mitochondria is mitochondria membrane potential (ΔΨm). Therefore, pharmacological manipulation of ΔΨm can be a promising strategy to prevent neuronal cell death against brain insults. Based on these issues, we investigated here whether nobiletin, a Citrus polymethoxylated flavone, prevents neurotoxic neuronal calcium overload and cell death via regulating basal ΔΨm against neuronal insult in primary cortical neurons and pure brain mitochondria isolated from rat cortices. Results demonstrated that nobiletin treatment significantly increased cell viability against glutamate toxicity (100 µM, 20 min) in primary cortical neurons. Real-time imaging-based fluorometry data reveal that nobiletin evokes partial mitochondrial depolarization in these neurons. Nobiletin markedly attenuated mitochondrial calcium overload and reactive oxygen species (ROS) generation in glutamate (100 µM)-stimulated cortical neurons and isolated pure mitochondria exposed to high concentration of Ca2+ (5 µM). Nobiletin-induced partial mitochondrial depolarization in intact neurons was confirmed in isolated brain mitochondria using a fluorescence microplate reader. Nobiletin effects on basal ΔΨm were completely abolished in K+-free medium on pure isolated mitochondria. Taken together, results demonstrate that K+ influx into mitochondria is critically involved in partial mitochondrial depolarization-related neuroprotective effect of nobiletin. Nobiletin-induced mitochondrial K+ influx is probably mediated, at least in part, by activation of mitochondrial K+ channels. However, further detailed studies should be conducted to determine exact molecular targets of nobiletin in mitochondria.

Tangeretin Improves Glucose Uptake in a Coculture of Hypertrophic Adipocytes and Macrophages by Attenuating Inflammatory Changes.

Obesity is characterized by a state of chronic low-grade inflammation and insulin resistance, which are aggravated by the interaction between hypertrophic adipocytes and macrophages. In this study, we investigated the effects of tangeretin on inflammatory changes and glucose uptake in a coculture of hypertrophic adipocytes and macrophages. Tangeretin decreased nitric oxide production and the expression of interleukin (IL)-6, IL-1ß, tumor necrosis factor-α, inducible nitric oxide synthase, and cyclooxygenase-2 in a coculture of 3T3-L1 adipocytes and RAW 264.7 cells. Tangeretin also increased glucose uptake in the coculture system, but did not affect the phosphorylation of insulin receptor substrate (IRS) and Akt. These results suggest that tangeretin improves insulin resistance by attenuating obesity-induced inflammation in adipose tissue.

Metformin Promotes Apoptosis but Suppresses Autophagy in Glucose-Deprived H4IIE Hepatocellular Carcinoma Cells.

BACKGROUND: Metformin, a well-known anti-diabetic drug, has gained interest due to its association with the reduction of the prevalence of cancer in patients with type 2 diabetes and the anti-proliferative effect of metformin in several cancer cells. Here, we investigated the anti-proliferative effect of metformin with respect to apoptosis and autophagy in H4IIE hepatocellular carcinoma cells. METHODS: H4IIE rat cells were treated with metformin in glucose-free medium for 24 hours and were then subjected to experiments examining the onset of apoptosis and/or autophagy as well as the related signaling pathways. RESULTS: When H4IIE cells were incubated in glucose-free media for 24 hours, metformin and 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) reduced the viability of cells. Inhibition of AMP-activated protein kinase (AMPK) by compound C significantly blocked cell death induced by metformin or AICAR. Pro-apoptotic events (nuclear condensation, hydrolysis of intact poly ADP ribose polymerase and caspase-3) were stimulated by metformin and then suppressed by compound C. Interestingly, the formation of acidic intracellular vesicles, a marker of autophagy, was stimulated by compound C. Although the deprivation of amino acids in culture media also induced apoptosis, neither metformin nor compound C affected cell viability. The expression levels of all of the autophagy-related proteins examined decreased with metformin, and two proteins (light chain 3 and beclin-1) were sensitive to compound C. Among the tested inhibitors against MAP kinases and phosphatidylinositol-3-kinase/mammalian target of rapamycin, SB202190 (against p38MAP kinase) significantly interrupted the effects of metformin. CONCLUSION: Our data suggest that metformin induces apoptosis, but suppresses autophagy, in hepatocellular carcinoma cells via signaling pathways, including AMPK and p38 mitogen-activated protein kinase.

Effects of dihydrotestosterone on rat dermal papilla cells in vitro.

Androgenetic alopecia involves the action of dihydrotestosterone (DHT) on dermal papilla cells (DPCs) that line the base of the hair follicle. However, the mechanism of DHT action is not completely understood. The effects of DHT on DPCs, regulatory cells that function in follicle growth and the hair cycle, were examined in immortalized cells derived from rat vibrissa follicles. DHT did not affect the proliferation of immortalized DPCs. However, flow cytometry analysis revealed that DHT increased cell-cycle arrest in these cells, which was accompanied by an increase in the p27(kip1) level and by decreases in cyclin E, cyclin D1, and cyclin-dependent kinase 2 levels. DHT treatment resulted in the phosphorylation and nuclear translocation of Smad2/3, a mediator of the transforming growth factor-ß (TGF-ß) signaling pathway, which leads to the catagen phase of the hair cycle. DHT also induced the phosphorylation and nuclear translocation of heat shock protein 27 (HSP27). Moreover, DHT decreased the levels of total and nuclear ß-catenin, an important regulator of hair growth and proliferation, while lithium chloride, a glycogen synthase kinase-3ß inhibitor, attenuated the DHT-induced downregulation of the ß-catenin level. On the other hand, DHT increased the phosphorylation of mammalian target of rapamycin (mTOR), a regulator of proliferation, in immortalized DPCs. These results illustrate that DHT could shorten the duration of the hair growth cycle by initiating cell-cycle arrest, downregulating the ß-catenin level, and upregulating the TGF-ß/Smad and HSP27 level, whereas activation of mTOR by DHT could attenuate the inhibition of hair growth cycle in immortalized DPCs.

Mild mitochondrial depolarization is involved in a neuroprotective mechanism of Citrus sunki peel extract.

Mitochondrial membrane potential (∆Ψm ) contributes to determining a driving force for calcium to enter the mitochondria. It has been demonstrated that even a small mitochondrial depolarization is sufficient to prevent mitochondrial calcium overload and the subsequent apoptosis. Therefore, mild mitochondrial depolarization has been recently evaluated as a novel mechanism of neuroprotection via inhibiting neurotoxic mitochondrial calcium overload during neuronal insults. In the present study, using both real-time recording and flow cytometric analyses of ∆Ψm , we demonstrated that ethanolic peel extract of Citrus sunki Hort. ex Tanaka (CPE) and its active compounds are capable of inducing a mild mitochondrial depolarization. Polymethoxylated flavones such as nobiletin and tangeretin were found as the active compounds responsible for CPE effects on ∆Ψm . Neuronal viability was significantly increased in a dose-dependent manner by CPE treatment in H2 O2 -stimulated HT-22 cells as an in vitro neuronal insult model. CPE treatment significantly inhibited H2 O2 -induced apoptotic processes such as chromatin condensation, caspase 3 activation and anti-poly (ADP-ribose) polymerase (PARP) cleavage. CPE treatment significantly blocked mitochondrial calcium overload in H2 O2 -stimulated HT-22 neurons as indicated by rhod-2 acetoxymethyl ester. Taken together, our findings suggest that CPE and its active compounds may be considered as promising neuroprotective agents via inducing a mild mitochondrial depolarization.

p-Synephrine stimulates glucose consumption via AMPK in L6 skeletal muscle cells.

Interest in p-synephrine, the primary protoalkaloid in the extract of bitter orange and other citrus species, has increased due to its various pharmacological effects and related adverse effects. The lipolytic activity of p-synephrine has been repeatedly revealed by in vitro and in vivo studies and p-synephrine is currently marketed as a dietary supplement for weight loss. The present study investigated the effect of p-synephrine on glucose consumption and its action mechanism in L6 skeletal muscle cells. Treatment of L6 skeletal muscle cells with p-synephrine (0-100µM) did not affect cell viability and increased basal glucose consumption up to 50% over the control in a dose-dependent manner. The basal- or insulin-stimulated lactic acid production as well as glucose consumption was significantly increased by the addition of p-synephrine. p-Synephrine stimulated the phosphorylation of AMPK but not of Akt. p-Synephrine-induced glucose consumption was sensitive to the inhibition of AMPK but not to the inhibition of PI3 kinase. p-Synephrine also stimulated the translocation of Glut4 from the cytoplasm to the plasma membrane; this stimulation was suppressed by the inhibition of AMPK, but not of PI3 kinase. Taken together, p-synephrine can stimulate glucose consumption (Glut4-dependent glucose uptake) by stimulating AMPK activity, regardless of insulin-stimulated PI3 kinase-Akt activity in L6 skeletal muscle cells.

Effects of brown alga, Ecklonia cava on glucose and lipid metabolism in C57BL/KsJ-db/db mice, a model of type 2 diabetes mellitus.

Recently, there has been a growing interest in alternative therapies of marine algae for diabetes. Therefore, the anti-diabetic effects of brown alga, Ecklonia cava was investigated in type 2 diabetic animal. Male C57BL/KsJ-db/db (db/db) mice were divided into control, dieckol rich extract of E. cava (AG-dieckol), or rosiglitazone (RG) groups. The blood glucose, blood glycosylated hemoglobin levels, and plasma insulin levels were significantly lower in the AG-dieckol and RG groups than in the control db/db mice group, while glucose tolerance was significantly improved in the AG-dieckol group. AG-dieckol markedly lowered plasma and hepatic lipids concentration compared to the control db/db mice group. The antioxidant enzyme activities were significantly higher in the AG-dieckol group than in the control db/db mice group, yet its TBARS level was markedly lower compared to the RG group. With regard to hepatic glucose regulating enzyme activities, glucokinase activity was enhanced in the AG-dieckol group mice, while glucose-6-phosphatase and phosphoenolpyruvate carboxykinase activities in the AG-dieckol group mice were significantly lowered than those in the control db/db mice group. These results suggest that AG-dieckol exert an anti-diabetic effect in type 2 diabetic mice by improving the glucose and lipid metabolism and antioxidant enzymes.

cAMP antagonizes ERK-dependent antiapoptotic action of insulin.

Insulin has antiapoptotic activity in various cell types. However, the signaling pathways underlying the antiapoptotic activity of insulin is not yet known. This study was conducted to determine if cAMP affects the antiapoptotic activity of insulin and the activity of PI3K and ERK in CHO cells expressing human insulin receptors (CHO-IR). Insulin-stimulated ERK activity was completely suppressed by cAMP-elevating agents like as pertussis toxin (Ptx) and cholera toxin (Ctx) after 4 h treatment. Insulin-stimulated PKB/Akt activity was not affected at all. Ptx treatment together with insulin increased the number of apoptotic cells and the degree of DNA fragmentation. Ctx or 8-brcAMP treatment also increased the number of apoptotic cells and stimulated the cleavage of caspase-3 and the hydrolysis of PARP. Taken together, cAMP antagonizes the antiapoptotic activity of insulin and the main target molecule of cAMP in this process is likely ERK, not PI3K-dependent PKB/Akt.

6-Hydroxydopamine-induced PC12 cell death is mediated by MEF2D down-regulation.

Recently, it was reported that in a 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model, neuronal cell death is associated with the cdk5-mediated hyperphosphorylation of myocyte enhancer factor 2 (MEF2), a transcription factor that is critically required for neuronal survival. In the present study, we investigated the possible involvement of cdk5-mediated MEF2D down-regulation on 6-hydroxydopamine (6-OHDA)-induced PC12 cell death. 6-OHDA was found to significantly increase nitric oxide (NO) production and to induce apoptosis in a time-dependent manner in PC12 cells. Furthermore, 6-OHDA was found to markedly reduce MEF2D levels under conditions that could induce PC12 cell apoptosis. In addition, PC12 cell death and MEF2D degradation by 6-OHDA were prevented by the cdk5 inhibitor roscovitine, but roscovitine could not restore the 6-OHDA-induced inactivation of Akt. These results suggest that the cell death and MEF2D degradation caused by 6-OHDA are dependent on cdk5 activity. On the other hand, roscovitine enhanced the 6-OHDA-induced activations of ERK1/2 and JNK, but reduced the 6-OHDA-induced activation of p38. These results suggest that PC12 cell death by 6-OHDA appears to be regulated by the down-regulation of MEF2D via some interaction between cdk5 and MAP kinase.

Anti-neuroinflammatory activity of nobiletin on suppression of microglial activation.

A growing body of evidence suggests that nobiletin (5,6,7,8,3',4'-hexamethoxy flavone) from the peel of citrus fruits, enhances the damaged cognitive function in disease animal models. However, the neuroprotective mechanism has not been clearly elucidated. Since nobiletin has shown anti-inflammatory effects in several tissues, we investigated whether nobiletin suppresses excessive microglial activation implicated in neurotoxicity in lipopolysaccharide (LPS)-stimulated BV-2 microglia cell culture models. Release of nitric oxide (NO), the major inflammatory mediator in microglia, was markedly suppressed in a dose-dependent manner following nobiletin treatment (1-50 µM) in LPS-stimulated BV-2 microglia cells. The inhibitory effect of nobiletin was similar to that of minocycline, a well-known microglial inactivator. Nobiletin significantly inhibited the release of the pro-inflammatory cytokine tumor necrosis factor (TNF-α) and interleukin-1ß (IL-1ß). LPS-induced phosphorylations of extracellular signal-regulated kinase (ERK), c-Jun NH(2)-terminal kinase (JNK), and p38 mitogen-activated protein kinases (MAPKs) were also significantly inhibited by nobiletin treatment. In addition, nobiletin markedly inhibited the LPS-induced pro-inflammatory transcription factor nuclear factor κB (NF-κB) signaling pathway by suppressing nuclear NF-κB translocation from the cytoplasm and subsequent expression of NF-κB in the nucleus. Taken together, these results may contribute to further exploration of the therapeutic potential and molecular mechanism of nobiletin in relation to neuroinflammation and neurodegenerative diseases.

Apoptosis inducing activity of fucoidan in HCT-15 colon carcinoma cells.

The antitumor activity of fucoidan from Fucus vesiculosus was investigated in human colon carcinoma cells. The crude fucoidan, a polysaccharide composed predominantly of sulfated fucose, markedly inhibited the growth of HCT-15 cells (human colon carcinoma cells). After HCT-15 cells were treated with fucoidan, several apoptotic events such as DNA fragmentation, chromatin condensation and increase of the population of sub-G1 hypodiploid cells were observed. In the mechanism of fucoidan-induced apoptosis, we examined changes in Bcl-2 and Bax protein expression levels and activation of caspases. Fucoidan decreased Bcl-2 expression, whereas the expression of Bax was increased in a time-dependent manner compared to the control. In addition, the active forms of caspase-9 and caspase-3 were increased, and the cleavage of poly(ADP-ribose) polymerase (PARP), a vital substrate of effector caspase, was observed. Furthermore, the induction of apoptosis was also accompanied by a strong activation of extracellular signal-regulated kinase (ERK) and p38 kinase and an inactivation of phosphatidylinositol 3-kinase (PI3K)/Akt in a time-dependent manner. These findings provide evidence demonstrating that the pro-apoptotic effect of fucoidan is mediated through the activation of ERK, p38 and the blocking of the PI3K/Akt signal pathway in HCT-15 cells. These data support the hypothesis that fucoidan may have potential in colon cancer treatment.

Chronic blockade of the angiotensin II receptor has a differential effect on adipose and vascular PAI-1 in OLETF rats.

Angiotensinogen (AGT) and plasminogen activator inhibitor-1 (PAI-1) are expressed in both vascular and adipose tissues. Angiotensin II (AG II) has an adipogenic effect and increases PAI-1 expression. To evaluate the chronic effects of AG II type 1 receptor (AT(1)R) antagonism on adipose mass and PAI-1 expression in vascular and adipose tissues, losartan (30mg/kg/day) was administered to Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of type 2 diabetes, for 20 weeks. Adipose mass and regional fat distribution in the abdomen did not change after chronic AT(1)R antagonism in OLETF rats. AGT and PAI-1 mRNA expressions in adipose tissue of OLETF rats were significantly increased compared with Long-Evans Tokushima Otsuka (LETO) rats, the normal control. Chronic losartan therapy further increased the level of adipose AGT in OLETF rats, but did not affect the level of adipose PAI-1 mRNA. In contrast, aortic PAI-1 expression in OLETF rats was attenuated by chronic losartan therapy. Our results have two implications. First, adipose tissue may be an important source of AG II in metabolic syndrome even after chronic losartan therapy. Second, chronic AT(1)R antagonism with losartan causes differential effects on vascular and adipose PAI-1 expression.

The cytotoxicity of eutigosides from Eurya emarginata against HL-60 promyelocytic leukemia cells.

Two phenolic glucosides, eutigoside B and eutigoside C were isolated from the fresh leaves of Eurya emarginata. These two phenolic glucosides exerted a significant inhibitory effect on the growth of HL-60 promyelocytic leukemia cells. Furthermore, when the HL-60 cells were treated with eutigoside C, several apoptotic characteristics such as DNA fragmentation, morphologic changes, and increase of the population of sub-G1 hypodiploid cells were observed. In order to understand the mechanism of apoptosis induction by eutigoside C, we examined the changes of Bcl-2 and Bax expression levels. The eutigoside C reduced Bcl-2 protein and mRNA levels, but slightly increased Bax protein and mRNA levels in a time-dependent manner. When we examined the activation of caspase-3, an effector of apoptosis, the eutigoside C increased the expression of active form (19-kDa) of caspase-3 and the increase of their activities was demonstrated by the cleavage of poly (ADP-ribose) polymerase, a substrate of caspase-3, to 85-kDa. The results suggest that the inhibitory effect of eutigoside C from E. emarginata on the growth of HL-60 appears to arise from the induction of apoptosis via the down-regulation of Bcl-2 and the activation of caspase.

The effects of thiazolidinedione treatment on the regulations of aquaglyceroporins and glycerol kinase in OLETF rats.

Aquaporins (AQPs) that transport glycerol in addition to water are classified as aquaglyceroporins (AQP3, 7, 9). AQP7 in the adipose tissue and AQP9 in the liver may coordinately contribute to the increase in hepatic gluconeogenesis in states of insulin resistance. Thiazolidinedione (TZD) has been shown to increase adipose AQP7 and induce glycerol kinase (GlyK) which is nearly absent in adipocytes. In the present study, we analyzed both GlyK and AQP gene expression in adipose and hepatic tissues, and AQP3 in kidneys from Long-Evans Tokushima Otsuka (LETO), Otsuka Long-Evans Tokushima Fatty (OLETF), and rosiglitazone (RSG)-treated OLETF (RSG-OLETF) rats. We also evaluated AQP9 protein expression in cultured human hepatoma cells treated with oleic acid, Wy14643, or RSG. A 2-week RSG treatment increased AQP7 mRNA levels in the mesenteric fat, but not in the epididymal fat of OLETF rats. Rosiglitazone treatment markedly increased GlyK expression in both fat depots, with a greater increase in the mesenteric fat. The magnitudes of GlyK induction by RSG were greater than that of AQP7 in both adipose tissues (P < .05, each). AQP9 and GlyK levels in the liver were not affected by RSG treatment in OLETF rats. Oleic acid and Wy14643 upregulated AQP9 protein expression in cultured human hepatoma cells in a dose-dependent manner. AQP3 mRNA levels tended to increase in the outer medulla of the RSG-OLETF rats. These results indicate that in the adipose tissue TZD has an important role in the glycerol metabolic pathway through the regulation of AQP and GlyK, especially by GlyK induction. Free fatty acids may directly enhance glycerol availability in the liver via the upregulation of AQP9 levels. Renal AQP3 may be related to the fluid retention caused by TZD.

Induction of the apoptosis of HL-60 promyelocytic leukemia cells by Eurya emarginata.

This study examined the inhibitory effect of Eurya emarginata extracts on the growth of cancer cells. The ethylacetate (EtOAc) fraction of the E. emarginata leaves markedly inhibited the growth of leukemia cells including HL-60. When the HL-60 cells were treated with its EtOAc fraction, DNA fragmentation and sub-G1 hypodiploid cells were observed. Moreover, the EtOAc fraction of E. emarginata reduced the c-Myc and Bcl-2 protein and mRNA levels in a time-dependent manner, whereas the Bax protein and mRNA expression levels were slightly increased. The results suggest that the inhibitory effect of E. emarginata on the growth of HL-60 appears to arise from the induction of apoptosis via the down-regulation of Bcl-2 and c-Myc expression with an increase in the Bax expression level.

Arsenic trioxide-induced apoptosis is independent of stress-responsive signaling pathways but sensitive to inhibition of inducible nitric oxide synthase in HepG2 cells.

Arsenic trioxide (As(2)O(3)) has been found to be remarkably effective in the treatment of patients with acute promyelocytic leukemia (APL). Although evidences for the proapoptotic activity of As(2)O(3) have been suggested in leukemic and other solid cancer cells, the nature of intracellular mechanisms is far from clear. In the present study, we investigated As(2)O(3) affect on the stress-responsive signaling pathways and pretreatment with antioxidants using HepG2 cells. When treated with micromolar concentrations of As(2)O(3), HepG2 cells became highly apoptotic paralleled with activation of caspase-3 and members of mitogen-activated protein kinases (MAPKs) including extracellular signal-regulated kinase (ERK) and c-jun NH(2)-terminal kinase (JNK) but not p38 MAP kinase. However, inhibition of each kinase activity failed to inhibit apoptosis by As(2)O(3). Addition of n-acetyl cysteine (NAC) or diphenyleneiodonium (DPI) effectively protected cells from apoptosis and significantly lowered As(2)O(3)-induced activation of caspase-3. However, neither NAC nor DPI was able to effect ERK or JNK activation induced by As(2)O(3). Guanidinoethyldisulfide dihydrochloride (GED) and 2-ethyl-2-thiopseudourea (ETU), known inhibitors of the inducible nitric oxide synthase (iNOS), also suppressed the apoptotic activity of As(2)O(3). These results suggest that As2O3 induces caspase-mediated apoptosis involving a mechanism generating oxidative stress. However, activation of some stress-responsive signaling pathways by As(2)O(3) may not be the major determinant in the course of apoptotic processes.