Effects Of Nobiletin Research Articles

Nobiletin Prevents Body Weight Gain and Bone Loss in Ovariectomized C57BL/6J Mice

Obesity and osteoporosis are associated with estrogen deficiency following menopause. Therefore, it is important to prevent and treat both disorders to maintain a healthy life in postmenopausal women. Nobiletin, a polymethoxylated flavone, exhibits various pharmacologic effects, including anti-tumor and anti-inflammatory activities. Therefore, in this study, we examined the effects of nobiletin on obesity, obesity-related metabolic disorders, and bone mass in ovariectomized (OVX) mice. Mice were divided into four groups and underwent sham operation or OVX. OVX mice were treated with 50 or 100 mg/kg nobiletin, or received vehicle alone (0.3% carboxyl methyl cellulose/0.5% dimethyl sulfoxide). Nobiletin decreased body weight gain and white adipose tissue weight in OVX mice. Nobiletin also decreased triglyceride levels, and tended to reduce plasma total cholesterol and glucose levels. Additionally, nobiletin prevented the reduction in bone mineral density of the trabecular region of the femur in OVX mice. Taken together, our results suggest that nobiletin improves adiposity, dyslipidemia, hyperglycemia, and prevents bone loss in OVX mice. Therefore, nobiletin is expected to have beneficial effects for the prevention and improvement of metabolic disorders and osteoporosis in postmenopausal women.

Nobiletin, a polymethoxy flavonoid, exerts anti-allergic effect by suppressing activation of phosphoinositide 3-kinase

Nobiletin is a polymethoxy flavonoid present in fruit tissues of citrus species and has been reported to suppress degranulation of RBL-2H3 cells. However, the detailed mechanism is still unknown. In this study the mechanism of suppressive effect of nobiletin on degranulation of RBL-2H3 cells was examined. Nobiletin suppressed degranulation of both RBL-2H3 cells and bone marrow-derived mast cells induced by antigen stimulation. Nobiletin also suppressed degranulation stimulated by the calcium ionophore A23187 and thapsigargin, a specific inhibitor of the Ca2+-dependent ATPase. Elevation of intracellular free Ca2+ concentration was also suppressed by nobiletin when RBL-2H3 cells were stimulated by either antigen or A23187. Immunoblot analysis revealed that the inhibitory effect results from down-regulated phosphorylation of both phosphatidylinositol 3-kinase (PI3K) and phospholipase Cγ1 in the signaling pathways related to degranulation stimulated by antigen. Furthermore, oral administration of nobiletin suppressed vascular permeability in passive cutaneous anaphylaxis model mice. The tendency in all experiments obtained by treating with nobiletin was highly similar to that obtained by wortmannin, a specific inhibitor of PI3K. These findings suggest that nobiletin suppresses Ca2+ influx and consequently exerts the anti-allergy activity in a similar way to wortmannin.

The citrus flavonoid nobiletin inhibits proliferation and induces apoptosis in human pancreatic cancer cells in vitro

The cellular effects of nobiletin on human pancreatic cancer cells (PANC-1) and the mechanisms by which nobiletin inhibits the proliferation of these cells were investigated. A MTT assay and flow cytometry were used to examine cell proliferation and apoptosis, respectively. A Western blot assay was used to examine expression levels of the apoptotic proteins bax, bcl-2, and p53. NOB induced apoptosis in these cells via up-regulation of the proapoptotic protein bax and down-regulation of the antiapoptotic proteins bcl-2 and p53. The normal cell cycle of PANC-1 cells was arrested by NOB with a significant increase in the proportion of G0/G1 phase cells (p<0.05) and a significant decrease in the proportion of S phase cells (p<0.05). NOB can inhibit the proliferation of human pancreatic carcinoma cells by inducing apoptosis and arresting the cell cycle progression.

Stimulatory effect of nobiletin, a citrus polymethoxy flavone, on catecholamine synthesis through Ser19 and Ser40 phosphorylation of tyrosine hydroxylase in cultured bovine adrenal medullary cells

We previously reported the dual effects of nobiletin, a compound of polymethoxy flavones found in citrus fruits, on catecholamine secretion in cultured bovine adrenal medullary cells. Here, we report the effects of nobiletin on catecholamine synthesis in the cells. Nobiletin increased the synthesis of (14)C-catecholamines from [(14)C]tyrosine in a time (20-30min)- and concentration (1.0-100μM)-dependent manner. Nobiletin (10-100μM) also activated tyrosine hydroxylase activity. The stimulatory effect of nobiletin on (14)C-catecholamine synthesis was not observed when extracellular Ca(2+) was not present in the incubation medium. Protein kinase inhibitors including H-89, an inhibitor of cyclic AMP-dependent protein kinase, and KN-93, an inhibitor of Ca(2+)/calmodulin-dependent protein kinase II, suppressed the stimulatory effects of nobiletin on catecholamine synthesis as well as tyrosine hydroxylase activity. Nobiletin also induced the phosphorylation of tyrosine hydroxylase at Ser(19) and Ser(40). Nobiletin (1.0-100μM) inhibited (14)C-catecholamine synthesis induced by acetylcholine. The present findings suggest that nobiletin, by itself, stimulates catecholamine synthesis through tyrosine hydroxylase phosphorylation at Ser(19) and Ser(40), whereas it inhibits catecholamine synthesis induced by acetylcholine in bovine adrenal medulla.

Nobiletin and tangeretin ameliorate scratching behavior in mice by inhibiting the action of histamine and the activation of NF-κB, AP-1 and p38

Nobiletin and tangeretin are polymethoxy flavonoids that are abundantly present in the pericarp of Citrus unshiu (family Rutaceae) and the fruit of Citrus depressa (family Rutaceae). They exhibit various biological activities, including anti-inflammatory and anti-asthmatic effects. To evaluate the anti-allergic effects of nobiletin and tangeretin, we measured their inhibitory effects in histamine- or compound 48/80-induced scratching behavioral mice. Nobiletin and tangeretin potently inhibited scratching behavior, as well as histamine-induced vascular permeability. Furthermore, they inhibited the expression of the allergic cytokines, IL-4 and TNF-α as well as the activation of their transcription factors NF-κB, AP-1 and p38 in histamine-stimulated skin tissues. They also inhibited the expression of IL-4 and TNF-α and the activation of NF-κB and c-jun in PMA-stimulated RBL-2H3 cells. Furthermore, nobiletin and tangeretin inhibited protein kinase C (PKC) activity and the IgE-induced degranulation of RBL-2H3 cells. These agents showed potent anti-histamine effect through the Magnus test when guinea pig ileum was used. Based on these results, nobiletin and tangeretin may ameliorate scratching behavioral reactions by inhibiting the action of histamine as well as the activation of the transcription factors NF-κB and AP-1 via PKC.

Inhibitory Effects of Nobiletin on Hepatocellular Carcinoma In Vitro and In Vivo

Nobiletin (5, 6, 7, 8, 3' 4'-hexamethoxyflavone) is a major anticancer component in juice from zhishi (Rutaceae). This study aimed to investigate the inhibitory effect of Nobiletin on hepatic cancer cells both in vitro and in vivo. The 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT), growth curve, and clonogenic assay showed that nobiletin inhibited the proliferation of SMMC-7721 cells in vitro. Hoechst staining observed the characteristics of cell apoptosis in nobiletin-treated cells, and the apoptotic rates of treated groups were increased in a dose-dependent manner. Flow cytometric analysis demonstrated that nobiletin could block the cell cycle arrested at G2 phase. Cell cycle analysis was performed using flow cytometry. Results showed that cell cycle phase distribution analysis showed G2 arrest. It was found that nobiletin downregulated the expressions of Bcl-2 and COX-2 and up-regulated the expressions of Bax and caspase-3 in SMMC-7721 cells by western blotting. The experiment in vivo demonstrated that nobiletin significantly inhibited the growth of H22 transplantable tumor, downregulated the expressions of COX-2, up-regulated the expressions of Bax and caspase-3 detected by immunohistochemistry and western blotting, and the ratios of Bcl-2/Bax were decreased. Our results suggest that nobiletin has significant inhibitory effects on hepatocellular carcinoma both in vitro and in vivo.

Suppressive effect of nobiletin, a citrus polymethoxyflavonoid that downregulates thioredoxin-interacting protein expression, on tunicamycin-induced apoptosis in SK-N-SH human neuroblastoma cells

Increased expression of thioredoxin-interacting protein (TXNIP) has recently been proved to be a crucial event for irremediable endoplasmic reticulum (ER) stress resulting in the programmed cell death (apoptosis) of pancreatic β-cells. The present study demonstrated that treatment with 1–10μg/ml tunicamycin, a potent revulsant of ER stress, drastically induced TXNIP expression accompanied by the generation of cleaved caspase-3 as an indicator of apoptosis in SK-N-SH human neuroblastoma cells. This result substantiated that TXNIP is also involved in neurodegeneration triggered by ER stress. Moreover, we evaluated the effects of nobiletin, a citrus polymethoxyflavonoid, on tunicamycin-induced apoptosis and TXNIP expression in SK-N-SH cells, because we reported previously that this flavonoid might be able to reduce TXNIP expression. Co-treatment of SK-N-SH cells with 100μM nobiletin and 1μg/ml tunicamycin for 24h strongly suppressed apoptosis and increased TXNIP expression induced by 1μg/ml tunicamycin treatment alone. In addition, we proved that the ability of 100μM nobiletin treatment to reduce TXNIP expression is exerted from 3h after the onset of treatment. Therefore, the protective and ameliorative effects of nobiletin on neuronal degeneration and impaired memory, which several studies using animal models have demonstrated, might arise in part from nobiletin's ability to repress TXNIP expression

Nobiletin, a citrus flavonoid, ameliorates cognitive impairment, oxidative burden, and hyperphosphorylation of tau in senescence-accelerated mouse

Senescence-accelerated mouse prone 8 (SAMP8) is a model of aging characterized by the early onset of learning and memory impairment and various pathological features of Alzheimer's disease (AD). Our recent studies have demonstrated that nobiletin, a polymethoxylated flavone from citrus peels, ameliorates learning and memory impairment in olfactory-bulbectomized mice, amyloid precursor protein transgenic mice, and NMDA receptor antagonist-treated mice. Here, we present evidence that this natural compound improves age-related cognitive impairment and reduces oxidative stress and tau phosphorylation in SAMP8 mice. Treatment with nobiletin (10 or 50mg/kg) reversed the impairment of recognition memory and context-dependent fear memory in SAMP8 mice. Treatment with nobiletin also restored the decrease in the GSH/GSSG ratio in the brain of SAMP8 mice. In addition, increases in glutathione peroxidase and manganese-superoxide dismutase activities, as well as a decrease in protein carbonyl level, were observed in the brain of nobiletin-treated SAMP8 mice. Furthermore, nobiletin reduced tau phosphorylation in the hippocampus of SAMP8 mice. Together, the markedly beneficial effects of nobiletin represent a potentially useful treatment for ameliorating the learning and memory deficits, oxidative stress, and hyperphosphorylation of tau in aging as well as age-related neurodegenerative diseases such as AD.

Nobiletin Ameliorates the Deficits in Hippocampal BDNF, TrkB, and Synapsin I Induced by Chronic Unpredictable Mild Stress

Background. Our previous study has demonstrated that nobiletin could reverse the behavioral alterations in stressed mice. However, the relation of its antidepressant-like action with neurotrophic molecular expression remains unknown. This study aimed to explore the antidepressant-like mechanism of nobiletin related to the neurotrophic system in rats exposed to chronic unpredictable mild stress (CUMS). Methods. Depressive-like anhedonia (assessed by sucrose preference) and serum corticosterone secretion were evaluated in the CUMS, followed by brain-derived neurotrophic factor (BDNF), its tropomyosin-related kinase receptor B (TrkB), and the downstream target synapsin I expressions in the hippocampus. Results. Anhedonia, which occurred within week 2, was rapidly ameliorated by nobiletin. While fluoxetine needed additional 2 weeks to improve the anhedonia. In addition, nobiletin administration for 5 weeks significantly ameliorated CUMS-induced increase in serum corticosterone levels. Furthermore, we also found that CUMS-induced deficits of hippocampal BDNF, TrkB, and synapsin I were ameliorated by nobiletin. Conclusions. Taken together, these findings suggest that nobiletin produces rapidly acting antidepressant-like responses in the CUMS and imply that BDNF-TrkB pathway may play an important role in the antidepressant-like effect of nobiletin.

Nobiletin, a polymethoxyflavone in citrus fruits, reduces TAFI expression in HepG2 cells through transcriptional inhibition

Thrombin-activatable fibrinolysis inhibitor (TAFI, carboxypeptidase B2) is a 58-kDa plasma glycoprotein secreted by hepatocytes as an inactive form. TAFI is activated by the thrombin-thrombomodulin complex, and activated TAFI (TAFIa) plays an important role in regulating the balance between coagulation and fibrinolysis through inhibition of fibrinolysis. It has been suggested that high levels of TAFI in circulating plasma increase the risks of cardiovascular death and acute phase in ischaemic stroke. However, the mechanisms of regulating TAFI expression have been unclear. The present study investigated the effects of nobiletin (a polymethoxy flavonoid contained in the rind of citrus fruits) on TAFI gene (CPB2) and TAFI antigen expression in cultured human hepatoma HepG2 cells. Nobiletin decreased the release of TAFI antigen from HepG2 cells into conditioned medium in parallel with decreased levels of CPB2 mRNA and antigen. The half-life time of CPB2 mRNA in nobiletin-treated cells was unchanged compared to that of untreated control cells. Using nobiletin-treated cells that were transfected with a luciferase CPB2 promoter reporter plasmid, activity decreased to half of that in untreated control cells. A series of luciferase reporter constructs containing 5´-flanking region deletions of the human CPB2 gene showed that the sequences from -150 bp to -50 bp were essential for transcription of CPB2 and contained an AP-1 binding sequence at ~ -119 bp to - 99 bp in the CPB2 promoter. The amount of complexed nuclear protein and sequences from ~ -119 bp to -99 bp was decreased in nobiletin-treated cells. ChIP assays showed that c-Jun bound to the ~ -119 bp to -99 bp region of the CPB2 promoter and that the amount of the immunocomplex decreased after nobiletin treatment. Therefore, nobiletin-induced repression of CPB2 transcription might involve AP-1 inhibition and/or prevention of AP-1 binding in a specific region on the CPB2 gene in HepG2 cells.

Nobiletin improves obesity and insulin resistance in high-fat diet-induced obese mice

Nobiletin (NOB) is a polymethoxylated flavone present in citrus fruits and has been reported to have antitumor and anti-inflammatory effects. However, little is known about the effects of NOB on obesity and insulin resistance. In this study, we examined the effects of NOB on obesity and insulin resistance, and the underlying mechanisms, in high-fat diet (HFD)-induced obese mice. Obese mice were fed a HFD for 8weeks and then treated without (HFD control group) or with NOB at 10 or 100mg/kg. NOB decreased body weight gain, white adipose tissue (WAT) weight and plasma triglyceride. Plasma glucose levels tended to decrease compared with the HFD group and improved plasma adiponectin levels and glucose tolerance. Furthermore, NOB altered the expression levels of several lipid metabolism-related and adipokine genes. NOB increased the mRNA expression of peroxisome proliferator-activated receptor (PPAR)-γ, sterol regulatory element-binding protein-1c, fatty acid synthase, stearoyl-CoA desaturase-1, PPAR-α, carnitine palmitoyltransferase-1, uncoupling protein-2 and adiponectin, and decreased the mRNA expression of tumor necrosis factor-α and monocyte chemoattractant protein-1 in WAT. NOB also up-regulated glucose transporter-4 protein expression and Akt phosphorylation and suppressed IκBα degradation in WAT. Taken together, these results suggest that NOB improves adiposity, dyslipidemia, hyperglycemia and insulin resistance. These effects may be elicited by regulating the expression of lipid metabolism-related and adipokine genes, and by regulating the expression of inflammatory makers and activity of the insulin signaling pathway.

Antimetastatic effect of nobiletin through the down-regulation of CXC chemokine receptor type 4 and matrix metallopeptidase-9

Context: Nobiletin is one of the citrus bioflavonoids and can be found in citrus fruits such as lemons, oranges, tangerines, and grapefruits. The most studied properties of nobiletin are its anti-inflammatory and anticancer activities.Objective: The exact mechanisms of how nobiletin inhibits tumor metastasis and invasion are still not fully understood. In this study, we screened various natural compounds to down-modulate the CXC chemokine receptor-4 (CXCR4) and matrix metallopeptidase-9 (MMP-9).Materials and methods: The effect of nobiletin on the constitutive expressions of CXCR4 and MMP-9, MMP-9 enzymatic activity, associated nuclear factor κB (NF-κB) and mitogen-activated protein kinases (MAPKs) activation, and tumor cell invasion in human breast cancer cells was investigated. CXCR4 and MMP-9 expression were evaluated via reverse transcription polymerase chain reaction (RT-PCR) and western blotting. NF-κB activation was also evaluated by electrophoretic mobility shift assay (EMSA). In addition, the antimetastatic effects of nobiletin were determined by gelatin zymography and invasion assay.Results: Nobiletin down-regulated both the constitutive expressions of CXCR4 and MMP-9 in human breast cancer cells with IC50 values of 32 and 24 µM, respectively. Nobiletin also suppressed MMP-9 enzymatic activity and tumor cell invasion under noncytotoxic concentrations. Neither proteasome inhibition nor lysosomal stabilization had any effect on the nobiletin-induced decrease in CXCR4 expression. A detailed study of the underlying molecular mechanisms revealed that the regulation of the down-regulation of CXCR4 and MMP-9 were at the transcriptional level, as indicated by the down-regulation of mRNA expression and the suppression of the constitutive NF-κB and MAPKs activation.Discussion and conclusion: Our results indicate, for the first time, that nobiletin is a novel blocker of CXCR4 and MMP-9 expressions and thus has the potential to suppress metastasis of breast cancer.

Synergistic Anti-inflammatory Effects of Nobiletin and Sulforaphane in Lipopolysaccharide-Stimulated RAW 264.7 Cells

Inflammation plays important roles in the initiation and progress of many diseases including cancers in multiple organ sites. Herein, we investigated the anti-inflammatory effects of two dietary compounds, nobiletin (NBN) and sulforaphane (SFN), in combination. Noncytotoxic concentrations of NBN, SFN, and their combinations were studied in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophage cells. The results showed that combined NBN and SFN treatments produced much stronger inhibitory effects on the production of nitric oxide (NO) than NBN or SFN alone at higher concentrations. These enhanced inhibitory effects were synergistic based on the isobologram analysis. Western blot analysis showed that combined NBN and SFN treatments synergistically decreased iNOS and COX-2 protein expression levels and induced heme oxygenase-1 (HO-1) protein expression. Real-time polymerase chain reaction analysis indicated that low doses of NBN and SFN in combination significantly suppressed LPS-induced upregulation of IL-1 mRNA levels and synergistically increased HO-1 mRNA levels. Overall, our results demonstrated that NBN and SFN in combination produced synergistic effects in inhibiting LPS-induced inflammation in RAW 264.7 cells.

Protective Effects of Nobiletin on Hypertension and Cerebral Thrombosis in Stroke-Prone Spontaneously Hypertensive Rats (SHRSP)

Some citrus flavonoids have been reported to possess antioxidant activities that moderate endothelial dysfunction and show protective effects on cardiovascular disease. We have investigated the protective effects of nobiletin (5,6,7,8,3’,4’-hexamethoxy flavone) derived from the peel of Citrus depressa Hayata (Shiikuwasha), a citrus fruit produced in Okinawa prefecture in Japan on hypertension and thrombogenicity in cerebral vessels of stroke-prone spontaneously hypertensive rats (SHRSP). Nobiletin was added to the diet of male SHRSP (7 weeks old) for 4 weeks. The age-related increase in systolic blood pressure usually observed in SHRSP was significantly suppressed in the treated animals. Thrombogenesis in pial blood vessels, determined using a He-Ne laser technique, and antioxidant activity, assessed by measuring urinary 8-hydroxy-2’-deoxyguanosine (8-OHdG), were significantly reduced after treatment. Urinary nitric oxide (NO) metabolites and acetylcholine-induced endothelial relaxation were increased after dietary intervention. These results strongly suggested that antihypertensive and antithrombotic effects of nobiletin may be related to an increase in bioavailable NO, possibly mediated by the scavenging of reactive oxygen species (ROS).

Nobiletin suppresses adipocyte differentiation of 3T3-L1 cells by an insulin and IBMX mixture induction

BackgroundNobiletin is a citrus flavonoid which possesses the flavone structure with six methoxy groups. Although nobiletin has been reported to display anti-inflammatory, anti-tumor, and anti-diabetes activities, its effect on adipocyte differentiation remained unclear. In the present study, we investigated the effect of nobiletin on the differentiation of 3T3-L1 preadipocytes into adipocytes. Methods3T3-L1 preadipocytes were treated with nobiletin under various differentiation conditions. The effect of nobiletin on adipocyte differentiation was evaluated by oil red O staining, real-time RT-PCR, and Western blotting. ResultsNobiletin significantly suppressed the differentiation of 3T3-L1 preadipocytes into adipocytes, upon induction with insulin together with a cAMP elevator such as 3-isobutyl-1-methylxanthine (IBMX), by downregulating the expression of the gene encoding peroxisome proliferator-activated receptor (PPAR) γ2. In addition, nobiletin decreased the phosphorylation of cAMP-response element-binding protein (CREB) and strongly enhanced the phophorylation of signal transducer and activator of transcription (STAT) 5. General significanceNobiletin has a suppressive effect on the differentiation of preadipocytes into adipocytes when cells were induced with a general differentiation cocktail such as insulin, IBMX, and dexamethasone.

Nobiletin Suppresses Adipogenesis by Regulating the Expression of Adipogenic Transcription Factors and the Activation of AMP-Activated Protein Kinase (AMPK)

The objective of this study was to elucidate the effect of nobiletin (5,6,7,8,3',4'-hexamethoxyflavone) on adipogenesis in 3T3-L1 cells. To determine the effect of nobiletin on adipogenesis, preadipocyte differentiation was induced in the presence or absence of nobiletin (10-100 μM) for 4 days. The results revealed that nobiletin markedly inhibited lipid accumulation and glycerol-3-phosphate dehydrogenase (GPDH) activity and blocked the expression of adipogenic transcription factors, including peroxisome proliferator-activated receptors (PPARγ) and CCAAT/enhancer binding proteins (C/EBPα). Moreover, nobiletin significantly increased AMP-activated protein kinase (AMPK), a major regulator of cellular energy balance, phosphorylation, and intracellular reactive oxygen species (ROS) generation. This study also investigated the involvement of AMPK in the expression of a major transcription factor, PPARγ. It was found that pretreatment with compound C, a cell permeable inhibitor of AMPK, abolished the inhibitory effects of nobiletin on PPARγ expression. The results suggest that nobiletin exerts antiadipogenic effects through modulation of the PPARγ and AMPK signaling pathway and, therefore, may be a promising antiobesity agent.

Nobiletin, a polymethoxylated flavonoid from citrus, shows anti‐angiogenic activity in a zebrafish in vivo model and HUVEC in vitro model

Traditional Chinese medicinal herbs are a rich source of compounds with reported anti-inflammatory and anti-carcinogenic effects. Growing evidence shows the codependence of chronic inflammation and angiogenesis, and the potential benefits of targeting angiogenesis in the treatment of chronic inflammation and targeting inflammation in the treatment of diseases with impaired angiogenesis. We hypothesized that the anti-inflammatory activity of the natural compounds may owe at least some of its efficacy to their anti-angiogenic activity and hence we investigated the anti-angiogenic activity of these compounds in vivo in zebrafish embryos and in vitro in human umbilical vein endothelial cells (HUVECs). Nobiletin, a polymethoxylated flavonoid from citrus fruits, showed anti-angiogenic activity in both assays. Nobiletin inhibited the formation of intersegmental vessels (ISVs) in live transgenic zebrafish embryos expressing green fluorescent protein (GFP) in the vasculature. Cell cycle analysis of dissociated zebrafish embryo cells showed that nobiletin induced G0/G1 phase accumulation in a dose-dependent manner in GFP-positive endothelial cells. Nobiletin also dose-dependently induced VEGF-A mRNA expression. In HUVECs, nobiletin inhibited endothelial cell proliferation and, to a greater extent, tube formation in a dose-dependent manner. As in the in vivo study, nobiletin induced G0/G1 cell cycle arrest in HUVECs. However, this arrest was not accompanied by an increase in apoptosis, indicating a cytostatic effect of nobiletin. This study, for the first time, identifies nobiletin as having potent anti-angiogenic activity and suggests that nobiletin has a great potential for future research and development as a cytostatic anti-proliferative agent.

NOBILETIN TRANSIENTLY INCREASES THE PRODUCTION OF NITRIC OXIDE AND CHANGES THE ACTIVITY OF SUCCINATE DEHYDROGENASE IN HUMAN BLOOD LYMPHOCYTES

The citrus flavonoids exhibit abilities to modulate the inflammatory response and carcinogenesis via several different mechanisms. We have studied the effects of two major citrus flavonoids – nobiletin (5,6,7,8,3′,4′-hexamethoxyflavone), and sinensetin (5,6,7,3′,4′-pentamethoxyflavone) on the spontaneous synthesis of nitric oxide (NO), succinate dehydrogenase (SDH) activity and the copper redox state of cytochrome c oxidase in human peripheral blood lymphocytes. Our results showed that in contrast to sinensetin, nobiletin causes a transient enhancement in the production of NO, which leads to a subsequent compensatory elevation of cytochrome c oxidase and SDH. High positive correlation between NO production and level of oxidation of copper in cytochrome oxidase and inverse correlation with the activity of SDH were found. We propose that temporal alterations of mitochondrial enzymes could mediate immunomodulatory and anticarcinogenic effects of nobiletin. PRACTICAL APPLICATIONS Positive correlation between nitric oxide production and level of oxidation of copper in cytochrome oxidase and inverse correlation with the activity of succinate dehydrogenase (SDH) were found in peripheral blood lymphocytes after treatment of cells by nobiletin. These results demonstrate that the beneficial immunomodulatory and anticarcinogenic effects of nobiletin possibly involve the transient inhibition of mitochondrial respiratory chain and subsequent compensatory elevation of SDH activity. Our findings indicate new steps in the molecular mechanism of nobiletin effects, suggesting new potential pharmacological actions of nutritional citrus flavonoids.

Effects of Nobiletin on PhIP-Induced Prostate and Colon Carcinogenesis in F344 Rats

The current study was designed to investigate the effects of nobiletin (5,6,7,8,3′,4′-hexamethoxy flavone) on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced prostate and colon carcinogenesis. PhIP was administered to 6-wk-old F344 male rats intragastrically (100 mg/kg) twice a wk for 10 wk. The animals were given 0.05% nobiletin or the basal diet for 50 wk. At the end of the experiment, serum testosterone, estrogen, and leptin did not differ between the 2 groups. The body weights of nobiletin-treated rats were significantly higher than controls (P < 0.05), and feeding of nobiletin significantly reduced the relative prostate (P < 0.05) and testes (P < 0.05) weights as well as the Ki67 labeling index in the normal epithelium in the ventral prostate (P < 0.01). The incidence and multiplicity of adenocarcinomas in nobiletin-treated ventral prostate were 50% and 36%, respectively, of controls, but the differences were not statistically significant. However, nobiletin did significantly reduce the total number of colonic aberrant crypt foci (ACF) compared to the control value (P < 0.05). Nobiletin, therefore, may have potential for chemoprevention of early changes associated with carcinogenesis in both the prostate and colon.

Regulation of adipocytokine secretion and adipocyte hypertrophy by polymethoxyflavonoids, nobiletin and tangeretin

AimsThe polymethoxyflavonoids nobiletin and tangeretin possess several important biological properties such as neuroprotective, antimetastatic, anticancer, and anti-inflammatory properties. The present study was undertaken to examine whether nobiletin and tangeretin could modulate adipocytokine secretion and to evaluate the effects of these flavonoids on the hypertrophy of mature adipocytes. Main methodsAll experiments were performed on the murine preadipocyte cell line 3T3-L1. We studied the formation of intracellular lipid droplets in adipocytes and the apoptosis-inducing activity to evaluate the effects of polymethoxyflavonoids on adipocyte differentiation and hypertrophy, respectively. The secretion of adipocytokines was measured using ELISA. Key findingsWe demonstrated that the combined treatment of differentiation reagents with nobiletin or tangeretin differentiated 3T3-L1 preadipocytes into adipocytes possessing less intracellular triglyceride as compared to vehicle-treated differentiated 3T3-L1 adipocytes. Both flavonoids increased the secretion of an insulin-sensitizing factor, adiponectin, but concomitantly decreased the secretion of an insulin-resistance factor, MCP-1, in 3T3-L1 adipocytes. Furthermore, nobiletin was found to decrease the secretion of resistin, which serves as an insulin-resistance factor. In mature 3T3-L1 adipocytes, nobiletin induced apoptosis; tangeretin, in contrast, did not induce apoptosis, but suppressed further triglyceride accumulation. SignificanceOur results suggest that nobiletin and tangeretin are promising therapeutic candidates for the prevention and treatment of insulin resistance by modulating the adipocytokine secretion balance. We also demonstrated the different effects of nobiletin and tangeretin on mature adipocytes.