Melinjo (Gnetum gnemon L.) Seed Extract Decreases Serum Uric Acid Levels in Nonobese Japanese Males: A Randomized Controlled Study

Resveratrol Improves Hyperuricemia and Ameliorates Renal Injury by Modulating the Gut Microbiota

Resveratrol (RES) has been reported to prevent hyperuricemia (HUA); however, its effect on intestinal uric acid metabolism remains unclear. This study evaluated the impact of RES on intestinal uric acid metabolism in mice with HUA induced by a high-fat diet (HFD). Moreover, we revealed the underlying mechanism through metagenomics, fecal microbiota transplantation (FMT), and 16S ribosomal RNA analysis. We demonstrated that RES reduced the serum uric acid, creatinine, urea nitrogen, and urinary protein levels, and improved the glomerular atrophy, unclear renal tubule structure, fibrosis, and renal inflammation. The results also showed that RES increased intestinal uric acid degradation. RES significantly changed the intestinal flora composition of HFD-fed mice by enriching the beneficial bacteria that degrade uric acid, reducing harmful bacteria that promote inflammation, and improving microbial function via the upregulation of purine metabolism. The FMT results further showed that the intestinal microbiota is essential for the effect of RES on HUA, and that Lactobacillus may play a key role in this process. The present study demonstrated that RES alleviates HFD-induced HUA and renal injury by regulating the gut microbiota composition and the metabolism of uric acid.

The Therapeutic Efficacy and Mechanism of Action of Gnetin C, a Natural Compound from the Melinjo Plant, in a Preclinical Mouse Model of Advanced Prostate Cancer

The metastasis-associated protein 1/protein kinase B (MTA1/AKT) signaling pathway has been shown to cooperate in promoting prostate tumor growth. Targeted interception strategies by plant-based polyphenols, specifically stilbenes, have shown great promise against MTA1-mediated prostate cancer progression. In this study, we employed a prostate-specific transgenic mouse model with MTA1 overexpression on the background of phosphatase and tensin homolog (Pten) null (R26MTA1; Ptenf/f) and PC3M prostate cancer cells which recapitulate altered molecular pathways in advanced prostate cancer. Mechanistically, the MTA1 knockdown or pharmacological inhibition of MTA1 by gnetin C (dimer resveratrol) in cultured PC3M cells resulted in the marked inactivation of mammalian target of rapamycin (mTOR) signaling. In vivo, mice tolerated a daily intraperitoneal treatment of gnetin C (7 mg/kg bw) for 12 weeks without any sign of toxicity. Treatment with gnetin C markedly reduced cell proliferation and angiogenesis and promoted apoptosis in mice with advanced prostate cancer. Further, in addition to decreasing MTA1 levels in prostate epithelial cells, gnetin C significantly reduced mTOR signaling activity in prostate tissues, including the activity of mTOR-target proteins: p70 ribosomal protein S6 kinase (S6K) and eukaryotic translational initiation factor 4E (elF4E)-binding protein 1 (4EBP1). Collectively, these findings established gnetin C as a new natural compound with anticancer properties against MTA1/AKT/mTOR-activated prostate cancer, with potential as monotherapy and as a possible adjunct to clinically approved mTOR pathway inhibitors in the future.

Molecular Efficacy of Gnetin C as Dual-Targeted Therapy for Castrate-Resistant Prostate Cancer

SCOPE

Resistance of castrate-resistant prostate cancer (CRPC) to enzalutamide (Enz) involves the expression of constitutively active androgen receptor splice variant (AR-V7). In addition to altered AR pathways, CRPC is characterized by "non-AR-driven" signaling, which includes an overexpression of metastasis-associated protein 1 (MTA1). Combining natural compounds with anticancer drugs may enhance drug effectiveness while reducing adverse effects. In this study, the in vitro and in vivo anticancer effects of Gnetin C (GnC) alone and in combination with Enz against CRPC are examined.

METHODS AND RESULTS

The effects of GnC alone and in combination with Enz are assessed by cell viability, clonogenic survival, cell migration, and AR and MTA1 expression using 22Rv1 cells. The tumor growth in vivo is assessed by bioluminescent imaging, western blots, RT-PCR, and IHC. GnC alone and in combined treatment inhibit cell viability, clonogenic survival and migration, and AR and MTA1 expression in 22Rv1 cells. The underlying AR- and MTA1-targeted anticancer mechanisms of treatments in vivo involve inhibition of proliferation and angiogenesis, and induction of apoptosis.

CONCLUSION

The findings demonstrate that GnC alone and GnC combined with Enz effectively inhibits AR- and MTA1-promoted tumor-progression in advanced CRPC, which indicates its potential as a novel therapeutic approach for CRPC.

A Randomized Trial on Resveratrol Supplement Affecting Lipid Profile and Other Metabolic Markers in Subjects with Dyslipidemia

Resveratrol is a polyphenol with a well-established beneficial effect on dyslipidemia and hyperuricemia in preclinical experiments. Nonetheless, its efficacy and dose-response relationship in clinical trials remains unclear. This study examined whether resveratrol supplement improves the serum lipid profile and other metabolic markers in a dose-response manner in individuals with dyslipidemia. A total of 168 subjects were randomly assigned to placebo (n = 43) and resveratrol treatment groups of 100 mg/d (n = 41), 300 mg/d (n = 43), and 600 mg/d (n = 41). Anthropometric and biochemical parameters were analyzed at baseline and 4 and 8 weeks. Resveratrol supplementation for 8 weeks did not significantly change the lipid profile compared with the placebo. However, a significant decrease of serum uric acid was observed at 8 weeks in 300 mg/d (-23.60 ± 61.53 μmol/L, p < 0.05) and 600 mg/d resveratrol groups (-24.37 ± 64.24 μmol/L, p < 0.01) compared to placebo (8.19 ± 44.60 μmol/L). Furthermore, xanthine oxidase (XO) activity decreased significantly in the 600 mg/d resveratrol group (-0.09 ± 0.29 U/mL, p < 0.05) compared with placebo (0.03 ± 0.20 U/mL) after 8 weeks. The reduction of uric acid and XO activity exhibited a dose-response relationship (p for trend, <0.05). Furthermore, a marked correlation was found between the changes in uric acid and XO activity in the resveratrol groups (r = 0.254, p < 0.01). Resveratrol (10 μmol/L) treatment to HepG2 cells significantly reduced the uric acid levels and intracellular XO activity. Nevertheless, we failed to detect significant differences in glucose, insulin, or oxidative stress biomarkers between the resveratrol groups and placebo. In conclusion, resveratrol supplementation for 8 weeks had no significant effect on lipid profile but decreased uric acid in a dose-response manner, possibly due to XO inhibition in subjects with dyslipidemia. The trial was registered on ClinicalTrials.gov (NCT04886297).

Gnetin C Intercepts MTA1-Associated Neoplastic Progression in Prostate Cancer

Nutritional chemoprevention is particularly suitable for prostate cancer. Gnetin C, a resveratrol dimer found abundantly in the melinjo plant (Gnetum gnemon), may possess more potent biological properties compared to other stilbenes. We examined the effects of gnetin C in a high-risk premalignant transgenic mouse model overexpressing tumor-promoting metastasis-associated protein 1 (MTA1) on the background of Pten heterozygosity (R26^MTA1; Pten^+/f; Pb-Cre⁺). Mice were fed diets supplemented with the following compounds: pterostilbene (70 mg/kg diet); gnetin C, high dose (70 mg/kg diet); and gnetin C, low dose (35 mg/kg diet). Prostate tissues were isolated after 17 weeks and examined for histopathology and molecular markers. Serum was analyzed for cytokine expression. Gnetin C-supplemented diets substantially delayed the progression of preneoplastic lesions compared to other groups. Prostate tissues from gnetin C-fed mice showed favorable histopathology, with decreased severity and number of prostatic intraepithelial neoplasia (PIN) foci, reduced proliferation, and angiogenesis. A decreased level of MTA1, concurrent with the trend of increasing phosphatase and tensin homolog expression and reduced interleukin 2 (IL-2) levels in sera, were also detected in gnetin C-fed mice. Importantly, gnetin C did not exert any visible toxicity in mice. Our findings demonstrate that a gnetin C-supplemented diet effectively blocks MTA1-promoted tumor progression activity in high-risk premalignant prostate cancer, which indicates its potential as a novel form of nutritional interception for prostate cancer chemoprevention.

Resveratrol supplementation efficiently improves endothelial health: A systematic review and meta-analysis of randomized controlled trials

We perform a systematic review and meta-analysis of randomized controlled trials (RCTs) to quantify the effect of resveratrol supplementation on endothelial function. A comprehensive search was performed in electronic databases including PubMed, Scopus, Web of Science, and Cochrane Library up to February 2021 with no limitation in time and language. A meta-analysis of eligible studies was performed using a random-effects model to estimate the pooled effect size of flow-mediated dilation (FMD), intracellular adhesion molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1), fibrinogen, and plasminogen activator inhibitor-1 (PAI-1). In total, 21 arms from 17 studies were included. The meta-analysis results showed that resveratrol significantly change the concentrations of FMD (WMD: 1.43%; 95% CI: 0.98 to 1.88, p < .001) and ICAM-1 (WMD: -7.09 ng/ml, 95% CI: -7.45 to -6.73, p < .001). However, VCAM-1, fibrinogen, and PAI-1 did not change significantly after resveratrol supplementation. In conclusion, the results of this study suggest that resveratrol supplementation can improve endothelial function which could be important, especially in patients with cardiovascular diseases.

Therapeutic Potential of Gnetin C in Prostate Cancer: A Pre-Clinical Study

Natural stilbenes have gained significant attention in the scientific community owing to their potential anticancer effects against prostate cancer. We recently reported that Gnetin C, a resveratrol (Res) dimer, demonstrated more potent inhibition of metastasis-associated protein 1/v-ets avian erythroblastosis virus E26 oncogene homolog 2 (MTA1/ETS2) axis in prostate cancer cell lines than other stilbenes. In this study, we investigated in vivo antitumor effects of Gnetin C in two doses (50 and 25 mg/kg, i.p.) using PC3M-Luc subcutaneous xenografts and compared these to Res and pterostilbene (Pter). We found that while vehicle-treated mice revealed rapid tumor progression, compounds-treated mice showed noticeable delay in tumor growth. Gnetin C in 50 mg/kg dose demonstrated the most potent tumor inhibitory effects. Gnetin C in 25 mg/kg dose exhibited tumor inhibitory effects comparable with Pter in 50 mg/kg dose. Consistent with the effective antitumor effects, Gnetin C-treated tumors showed reduced mitotic activity and angiogenesis and a significant increase in apoptosis compared to all the other groups. The data suggest that Gnetin C is more potent in slowing tumor progression in prostate cancer xenografts than Res or Pter. Taken together, we demonstrated, for the first time, that Gnetin C is a lead compound among stilbenes for effectively blocking prostate cancer progression in vivo.

Structural Studies on Stilbene Oligomers Isolated from the Seeds of Melinjo (Gnetum gnemon L.)

This paper describes the isolation and structural determination of a new stilbene dimer, named 7a-epi-gnetin C, from melinjo (Gnetum gnemon L.) seed extract. The relative structure was elucidated based on NMR spectroscopic evidence, while the absolute configuration was assigned by a combination of NMR and electronic circular dichroism spectroscopic analysis and chemical conversion. 7a-epi-Gnetin C was evaluated as an antioxidant and was shown to have a comparable activity to the known stilbene oligomers. In addition, the structural revision of gnetin L, a known stilbene dimer, was also discussed.

Neuroprotective Properties of Resveratrol and Its Derivatives-Influence on Potential Mechanisms Leading to the Development of Alzheimer's Disease

The lack of effective Alzheimer's disease treatment is becoming a challenge for researchers and prompts numerous attempts to search for and develop better therapeutic solutions. Compounds that affect several routes of the neurodegeneration cascade leading to the development of disease are of particular interest. An example of such substances is resveratrol and its synthetic and natural derivatives, which have gained popularity in recent years and show promise as a possible new therapeutic option in the approach to Alzheimer's disease treatment. In this article, the state of the art evidence on the role of resveratrol (RSV) in neuroprotection is presented; research results are summarized and the importance of resveratrol and its derivatives in the treatment of Alzheimer's disease are underlined. It also focuses on various modifications of the resveratrol molecule that should be taken into account in the design of future research on drugs against Alzheimer's disease.

Melinjo seed extract increases adiponectin multimerization in physiological and pathological conditions

Melinjo seed extract (MSE) contains large amounts of polyphenols, including dimers of trans-resveratrol (e.g. gnetin C, L, gnemonoside A, B and D), and has been shown to potentially improve obesity. However, there is no clinical evidence regarding the anti-obesity effects of MSE, and its mechanisms are also unclear. We investigated the hypothesis that MSE supplementation increases the adiponectin (APN) multimerization via the up-regulation of disulfide bond A oxidoreductase-like protein (DsbA-L) under either or both physiological and obese conditions. To investigate the effect of MSE on the physiological condition, 42 healthy young volunteers were enrolled in a randomized, double-blind placebo-controlled clinical trial for 14 days. The participants were randomly assigned to the MSE 150 mg/day, MSE 300 mg/day or placebo groups. Furthermore, in order to investigate the effect of MSE on APN levels under obese conditions, we administered MSE powder (500 or 1000 mg/kg/day) to control-diet- or high-fat-diet (HFD)-fed C57BL/6 mice for 4 weeks. All participants completed the clinical trial. The administration of MSE 300 mg/day was associated with an increase in the ratio of HMW/total APN in relation to the genes regulating APN multimerization, including DsbA-L. Furthermore, this effect of MSE was more pronounced in carriers of the DsbA-L rs191776 G/T or T/T genotype than in others. In addition, the administration of MSE to HFD mice suppressed their metabolic abnormalities (i.e. weight gain, increased blood glucose level and fat mass accumulation) and increased the levels of total and HMW APN in serum and the mRNA levels of ADIPOQ and DsbA-L in adipose tissue. The present study suggests that MSE may exert beneficial effects via APN multimerization in relation to the induction of DsbA-L under both physiological and obese conditions.

MTA1-Dependent Anticancer Activity of Gnetin C in Prostate Cancer

The overexpression of metastasis-associated protein 1 (MTA1) in prostate cancer (PCa) contributes to tumor aggressiveness and metastasis. We have reported the inhibition of MTA1 by resveratrol and its potent analog pterostilbene in vitro and in vivo. We have demonstrated that pterostilbene treatment blocks the progression of prostatic intraepithelial neoplasia and adenocarcinoma in mouse models by inhibiting MTA1 expression and signaling. In the current study, we investigated the MTA1 targeted anticancer effects of Gnetin C, a resveratrol dimer, in comparison with resveratrol and pterostilbene. Using DU145 and PC3M PCa cells, we found that Gnetin C downregulates MTA1 more potently than resveratrol and pterostilbene. Further, Gnetin C demonstrated significant MTA1-mediated inhibitory effect on cell viability, colony formation, and migration, while showing a more potent induction of cell death than resveratrol or pterostilbene. In addition, we identified Gnetin C-induced substantial ETS2 (erythroblastosis E26 transformation-specific 2) downregulation, which is not only MTA1-dependent, but is also independent of MTA1 as a possible mechanism for the superior anticancer efficacy of Gnetin C in PCa. Together, these findings underscore the importance of novel potent resveratrol dimer, Gnetin C, as a clinically promising agent for the future development of chemopreventive and possibly combinatorial therapeutic approaches in PCa.

Immunomodulatory and Metabolic Changes after Gnetin-C Supplementation in Humans

Gnetin-C is a naturally occurring stilbene derived from the seeds of Gnetum gnemon L., an edible plant native to Southeast Asia that is called melinjo. Although the biological properties and safety of G. gnemon extract, which contains nearly 3% Gnetin-C, have been confirmed in various human studies, whether or not pure Gnetin-C is safe for humans is unclear at present. We conducted a randomized, double-blind, placebo-controlled trial. Healthy subjects were randomly divided into two groups. The interventional group (n = 6) was given Gnetin-C, and the control group (n = 6) was provided a placebo, for 14 days. Lipid profiles, biomarkers of oxidative stress and circulating blood cells were assessed before and after the intervention. All subjects completed the study, with no side effects reported across the study duration. Gnetin-C supplementation demonstrated a statistically significant increase in the absolute number of circulating natural killer (NK) cells expressing the activating receptors NKG2D and NKp46. NK cells derived from subjects who received Gnetin-C for two weeks showed higher cytotoxicity against K562 target cells than those before receiving Gnetin-C. In addition, Gnetin-C also resulted in a significant decrease in the absolute neutrophil count in the blood compared with the placebo. Furthermore, Gnetin-C significantly reduced the levels of uric acid, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, total adiponectin, and high-molecular-weight adiponectin. These data indicate that Gnetin-C has biological effects of enhancing the NK activity on circulating human immune cells. The immunomodulatory effects are consistent with a putative improvement in cancer immunosurveillance via the upregulation of the NKG2D receptor. The study was registered with UMIN-CTR, number 000030364, on 12 December 2017.

The effects of resveratrol intake on weight loss: a systematic review and meta-analysis of randomized controlled trials

This systematic review and meta-analysis of randomized controlled trials (RCTs) was conducted to summarize the effect of resveratrol intake on weight loss. We searched the following databases until July 2018: MEDLINE, EMBASE, Web of Science and Cochrane Central Register of Controlled Trials. Data were pooled using the inverse variance method and expressed as standardized mean difference (SMD) with 95% confidence intervals (95% CI). Out of 831 reports, 36 RCTs were eligible for including to our meta-analysis. The pooled results, using random-effects model showed that resveratrol supplementation significantly decreased body weight (SMD = -0.17; 95% CI, -0.33, -0.01; P = 0.03; I²: 62.6), body mass index (BMI) (SMD = -0.20; 95% CI, -0.35, -0.05; P = 0.01; I²: 60.6), fat mass (SMD = -0.32; 95% CI, -0.62, -0.03; P = 0.03; I²: 77.9) and waist circumference (WC) (SMD = -0.42; 95% CI, -0.68, -0.16; P = 0.001; I²: 75.2), and significantly increased lean mass (SMD = 1.21; 95% CI, 0.75, 1.67; P < 0.001; I²: 87.6). We found no significant effect of resveratrol administration on leptin (SMD = -0.20; 95% CI, -0.68, 0.27; P = 0.40; I²: 85.3) and adiponectin levels (SMD = 0.08; 95% CI, -0.39, 0.55; P = 0.74; I²: 91.0). Resveratrol supplementation significantly decreased body weight in obese patients (SMD -0.43; 95% CI, -0.60, -0.26) compared with other diseases (SMD 0.02; 95% CI, -0.29, 0.33), and type 2 diabetes mellitus (SMD -0.17; 95% CI, -0.37, 0.02). Overall, the current meta-analysis demonstrated that resveratrol intake significantly reduced weight, BMI, WC and fat mass, and significantly increased lean mass, but did not affect leptin and adiponectin levels.

Antiplasmodial Activity of Gnetum gnemon Leaves and Compounds Isolated from them

Gnetum gnemon L. (Gnetaceae) is used traditionally for treating malaria related fever by indigenous people of North East India. In our preliminary study, the ethanol extract of G. gnemon leaves showed promising antiplamodial activity against Plasmodium falciparum chloroquine sensitive (3D7) strain in vitro with an IC50 value of 29.4 μg/mL. Therefore, it was further investigated, and by following a bioassay guided approach, 2,3-dihydroxypropyl icosanoate (1), oleic acid (2) and ursolic acid (3) were isolated for the first time from this plant. Compound 3 showed highest antiplasmodial activity with IC50 values of 4.0 and 6.0 μg/mL against chloroquine sensitive (3D7) and resistant (Dd2) strains of P. falciparum, respectively. The antiplasmodial activity of 1 (IC50 9.5 and 11.4 μg/mL) and 2 (IC50 17.6 and 21.1 μg/mL) was moderate. The isolated constituents showed low cytotoxicity against rat skeletal muscle (L6) and human cervical cancer (HeLa) cells. This is the first report on the antimalarial potential of G. gnemon and the isolated compounds may be responsible for its activity. The findings of the study are in line with the ethnopharmacological claim and can be possible leads for future studies.

Melinjo (Gnetum gnemon L.) seed extract induces uncoupling protein 1 expression in brown fat and protects mice against diet-induced obesity, inflammation, and insulin resistance

Dietary supplementation with melinjo (Gnetum gnemon L.) seed extract (MSE) has been proposed as an anti-obesity strategy. However, it remains unclear how MSE modulates energy balance. We tested the hypothesis that dietary MSE reduces energy intake and/or increases physical activity and metabolic thermogenesis in brown and white adipose tissue (BAT and WAT) in mice. Twenty-four C57BL/6 J mice were provided with normal diet, high-fat diet (HFD), or HFD with 1% MSE added, for 17 weeks. Food intake, spontaneous locomotor activity, hepatic triglyceride (TG) content, and blood parameters were examined. Mitochondrial thermogenesis-associated molecule and inflammatory marker expression levels in BAT and WAT were examined by quantitative PCR and western blotting. Dietary MSE did not affect energy intake or spontaneous locomotor activity, but significantly suppressed HFD-induced fat accumulation, hyperglycemia, and hyperinsulinemia. Homeostasis model assessment of insulin resistance score and hepatic TG content were both lower in the MSE-supplemented HFD-fed group than in the HFD-fed group, indicating reduced insulin resistance and a less fatty liver. Dietary MSE upregulated thermogenic uncoupling protein 1 (UCP1) and mitochondrial marker cytochrome c oxidase subunit IV protein expression in BAT; this was closely associated with sirtuin 1 mRNA induction. mRNAs of adipose inflammatory markers, such as monocyte chemotactic 1 and interleukin-1, were induced by HFD but suppressed by MSE. Considering that UCP1 protein expression is the most physiologically relevant parameter to assess the thermogenic capacities of BAT, our results indicate that dietary MSE supplementation induces BAT thermogenesis and reduces obesity-associated adipose tissue inflammation, hepatic steatosis, and insulin resistance.

Structure-activity relationships of fraxamoside as an unusual xanthine oxidase inhibitor

Fraxamoside, a macrocyclic secoiridoid glucoside featuring a hydroxytyrosol group, was recently identified as a xanthine oxidase inhibitor (XOI) comparable in potency in vitro to the standard antigout drug allopurinol. However, this activity and its considerably higher value than its derivatives oleuropein, oleoside 11-methyl ester, and hydroxytyrosol are not explained by structure-activity relationships (SARs) of known XOIs. To exclude allosteric mechanisms, we first determined the inhibition kinetic of fraxamoside. The resulting competitive mechanism prompted a computational SAR characterization, combining molecular docking and dynamics, which fully explained the behavior of fraxamoside and its derivatives, attributed the higher activity of the former to conformational properties of its macrocycle, and showed a substantial contribution of the glycosidic moiety to binding, in striking contrast with glycoside derivatives of most other XOIs. Overall, fraxamoside emerged as a lead compound for a new class of XOIs potentially characterized by reduced interference with purine metabolism.

Effects of resveratrol supplementation on risk factors of non-communicable diseases: A meta-analysis of randomized controlled trials

The results of randomized controlled trials (RCTs) investigating resveratrol supplementation on risk factors of non-communicable diseases (NCDs) have been inconsistent. The present meta-analysis aimed to quantitatively evaluate the effects of resveratrol intervention on risk factors of NCDs. PubMed and Scopus databases were searched up to June 2017. Weighted mean differences were calculated for net changes in risk factors of NCDs by using a random-effects model. Pre-specified subgroup and univariate meta-regression analyses were carried out to explore the sources of heterogeneity. Twenty-nine studies (30 treatment arms) with 1069 participants were identified. Resveratrol supplementation significantly reduced the concentrations of fasting glucose (-4.77 mg/dL; 95% CI: -9.33 to -0.21 mg/dL; P = 0.040), total cholesterol (TC) (-9.75 mg/dL; 95% CI: -17.04 to -2.46 mg/dL; P = 0.009), and C-reactive protein (CRP) (-0.81 mg/L; 95% CI: -1.42 to -0.21 mg/L; P = 0.009). Resveratrol intervention exerted significant reductions in systolic blood pressure (SBP) and diastolic blood pressure (DBP) in subjects with type 2 diabetes mellitus (T2DM). Subgroup analysis also showed that the trials with resveratrol intervention ≥3 months significantly reduced the low-density lipoprotein cholesterol (LDL-C), DBP, and glycated hemoglobin (HbA1c) values. The results did not support that resveratrol intervention had favorable effects in altering high-density lipoprotein cholesterol (HDL-C), triglyceride (TAG), and homeostasis model assessment of insulin resistance (HOMA-IR). The present study provides substantial evidence that resveratrol supplementation has favorable effects on several risk factors of NCDs.

Fractionation using adsorptive macroporous resin HPD-600 enhances antioxidant activity of Gnetum gnemon L. seed hard shell extract

In this study, antioxidant activities and identification of the bioactive substances in Gnetum gnemon L. (Gg) seed hard shell were evaluated. The seed of Gnetum gnemon L., an Indonesian native plant, is commonly consumed as a vegetable or further processed as cracker. Isolated substances from Gnetum gnemon seed are mainly stilbenoid derivatives which show potent antioxidant, tyrosinase inhibitor, and antimicrobial activities. Nevertheless, the antioxidant activity of its crude extract is still considered weak. In this study, an effort was made to improve antioxidant potency by fractionation using macroporous adsorptive resin (MAR). This fractionation successfully enhanced antioxidant activity of red Gg seed hard shell extract with efficient adsorption contact time within 30 min. Antioxidant activity of fractions 25-75% v/v ethanol increased three- to sevenfold as compared to crude extract and more importantly resulted in dry product which was easier for further processes. Identification of bioactive compounds in Gg seed hard shell extract with different degrees of ripeness was also performed by HPLC and confirmed the presence of Gnetin C, resveratrol, and other stilbenoid derivatives. These other stilbenoid derivatives could be the main substances contributing in antioxidant action with lower IC₅₀ as compared to both Gnetin C and resveratrol. In summary, fractionation process using MAR HPD-600 reduced unnecessary sugar molecules from red Gg seed hard shell extract hence resulting to fraction with strong antioxidant activity.

Gnetin-C and other resveratrol oligomers with cancer chemopreventive potential

Resveratrol has been extensively studied to investigate its biological effects, including its chemopreventive potential against cancer. Over the past decade, various resveratrol oligomers, both naturally occurring and synthetic, have been described. These resveratrol oligomers result from the polymerization of two or more resveratrol units to form dimers, trimers, tetramers, or even more complex derivatives. Some oligomers appear to have antitumor activities that are similar or superior to monomeric resveratrol. In this review, we discuss resveratrol oligomers with anticancer potential, with emphasis on well-characterized compounds, such as the dimer gnetin-C and other oligomers from Gnetum gnemon, whose safety, pharmacokinetic, and biological activities have been studied in humans.

Melinjo (Gnetum gnemon) extract intake during lactation stimulates hepatic AMP-activated protein kinase in offspring of excessive fructose-fed pregnant rats

Excessive maternal fructose intake during pregnancy and in early postnatal life has metabolic consequences for the offspring. We investigated the effects of melinjo (Gnetum gnemon) extract (MeE) intake during lactation on the expression and phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) in the liver of offspring from excessive fructose-fed pregnant dams. Pregnant Wistar rats received a normal diet and 100g/L fructose solution during gestation ad libitum. At delivery, dams were divided into two groups: a control diet (FC) or a 0.1% MeE-containing diet (FM) fed during lactation. The dams that were not treated with fructose were fed a control diet (CC). At postnatal week 3, some pups were sacrificed, while the remaining continued to receive a normal diet and were sacrificed at week 17. Blood chemistry and phosphorylation levels of AMPK and acetyl-coenzyme A carboxylase (ACC) were evaluated. Plasma glucose levels in FC female offspring increased compared to that receiving CC at weeks 3 and 17; however, the levels in FM female offspring decreased at week 17. The insulin levels in FM female offspring decreased significantly compared to that in FC female offspring at week 3. Hepatic AMPK phosphorylation was upregulated in FM offspring at week 3 and in female, but not male, offspring at week 17. ACC phosphorylation in FM female offspring was upregulated at week 17. Our results suggest that maternal MeE intake during lactation may modulate the hepatic AMPK pathways in female offspring.

Antitumor activity of melinjo (Gnetum gnemon L.) seed extract in human and murine tumor models in vitro and in a colon-26 tumor-bearing mouse model in vivo

Melinjo (Gnetum gnemon L.) seed extract (MSE) and its active ingredient gnetin C (GC), a resveratrol dimer, have been shown to possess a broad spectrum of pharmacological activities. In this study, we investigated the antitumor activity of MSE and GC using human and murine tumor cell culture models in vitro. The antitumor activity of GC was compared with trans-resveratrol (tRV), a stilbenoid polyphenol. Our results show that MSE and GC at clinically achievable concentrations significantly inhibited the proliferation of pancreatic, prostate, breast, and colon cancer cell types (P < 0.05), without affecting normal cells. Interestingly, GC exerts enhanced antitumor activity than that of tRV (P < 0.05). MSE and GC significantly induced apoptosis in all the cancer cells, indicating MSE and GC inhibit tumor cell growth by inducing apoptosis (P < 0.001). Our findings provide evidence that MSE might induce apoptosis in cancer cells via caspase-3/7-dependent and -independent mechanisms. However, GC might trigger both early and late stage apoptosis in cancer cells, at least in part by activating caspase 3/7-dependent mechanisms. Furthermore, the antitumor efficacy of MSE observed in vitro was also validated in a widely used colon-26 tumor-bearing mouse model. Oral administration of MSE at 50 and 100 mg/kg per day significantly inhibited tumor growth, intratumoral angiogenesis, and liver metastases in BALB/c mice bearing colon-26 tumors (P < 0.05). In conclusion, our findings provide evidence that MSE and GC have potent antitumor activity. Most importantly, we provide the first evidence that MSE inhibits tumor growth, intratumoral angiogenesis, and liver metastasis in a colon-26 tumor-bearing mice.

Resveratrol derivative-rich melinjo (Gnetum gnemon L.) seed extract improves obesity and survival of C57BL/6 mice fed a high-fat diet

Melinjo (Gnetum gnemon L.) seed extracts (MSEs) are rich in resveratrol dimers (gnemonoside A, C, D, gnetin C), trans-resveratrol, and other resveratrol derivatives. trans-Resveratrol is a widely studied caloric restriction mimetic. In mice fed a high-fat diet (HFD), trans-resveratrol protects against obesity, type 2 diabetes, and premature death. Here, treatment of HFD-fed mice with 2.0% MSE significantly reduced body weight gain (p < 0.001), blood insulin (p < 0.01), and HOMA-IR (p < 0.05) after 8 weeks compared with untreated HFD-fed mice. Additionally, 0.2% MSE treatment of HFD-fed mice significantly improved physiological activity (p < 0.05) at 18 months of age and reduced risk of death due to HFD by 25% (hazard ratio = 0.75, p = 0.036). These data show that MSE can improve several aspects of metabolic syndrome and survival in mice and may have health benefits as a dietary supplement.

Resveratrol Derivative-Rich Melinjo Seed Extract Attenuates Skin Atrophy in Sod1-Deficient Mice

The oxidative damages induced by a redox imbalance cause age-related changes in cells and tissues. Superoxide dismutase (SOD) enzymes play a pivotal role in the antioxidant system and they also catalyze superoxide radicals. Since the loss of cytoplasmic SOD (SOD1) resulted in aging-like phenotypes in several types of murine tissue, SOD1 is essential for the maintenance of tissue homeostasis. Melinjo (Gnetum gnemon Linn) seed extract (MSE) contains trans-resveratrol (RSV) and resveratrol derivatives, including gnetin C, gnemonoside A, and gnemonoside D. MSE intake also exerts no adverse events in human study. In the present studies, we investigated protective effects of MSE on age-related skin pathologies in mice. Orally MSE and RSV treatment reversed the skin thinning associated with increased oxidative damage in the Sod1^−/− mice. Furthermore, MSE and RSV normalized gene expression of Col1a1 and p53 and upregulated gene expression of Sirt1 in skin tissues. In vitro experiments revealed that RSV significantly promoted the viability of Sod1^−/− fibroblasts. These finding demonstrated that RSV in MSE stably suppressed an intrinsic superoxide generation in vivo and in vitro leading to protecting skin damages. RSV derivative-rich MSE may be a powerful food of treatment for age-related skin diseases caused by oxidative damages.

Evaluation of the Antihyperuricemic Activity of Phytochemicals from Davallia formosana by Enzyme Assay and Hyperuricemic Mice Model

Abnormal serum urate levels are recognized as a critical factor in the progression of several chronic diseases. To evaluate the antihyperuricemic effect of Davallia formosana, the inhibitory activities of 15 isolated phytochemicals, including five novel compounds of 6,8-dihydroxychromone-7-C-β-d-glucopyranoside (1), 6,8,3′,4′-tetrahydroxyflavanone-7-C-β-d-glucopyranoside (2), 6,8,4′-trihydroxyflavanone-7-C-β-d-glucopyranoside (3), 8-(2-pyrrolidinone-5-yl)-catechin-3-O-β-d-allopyranoside (4), and epiphyllocoumarin-3-O-β-d-allopyranoside (5), were examined against xanthine oxidase (XOD) and in a potassium oxonate-(PTO-) induced acute hyperuricemic mice model. The results indicated that compounds 3 and 5 significantly inhibited XOD activity in vitro and reduced serum uric acid levels in vivo. This is the first report providing new insights into the antihyperuricemic activities of flavonoid glycosides which can possibly be developed into potential hypouricemic agents.

Pharmacokinetics and safety of resveratrol derivatives in humans after oral administration of melinjo (Gnetum gnemon L.) seed extract powder

Fruits and seeds of melinjo (Gnetum gnemon L.) are resveratrol derivative-rich materials. Pharmacokinetics of resveratrol derivatives in healthy volunteers after oral administration of 1000 mg of melinjo seed extract (MSE) powder were assessed and compared with those after oral dosing of trans-resveratrol (tRV) powder containing 4.8 mg of tRV only, equivalent to the content in 1000 mg MSE powder. Plasma tRV concentrations with enzymatic hydrolysis were maintained over 24 h, with a tmax of 12 h and a mean residence time (MRT) of 14 h, 5 and 2 times higher than those for tRV powder intake, respectively. Gnetin C, a resveratrol dimer, with hydrolysis was maintained in plasma for >96 h with a 36 h MRT. With repeated doses once daily for 28 days, plasma tRV and gnetin C concentrations with hydrolysis were in good agreement with the theoretical curves. MSE powder was well tolerated up to the oral dosing of 5000 mg with no serious adverse events.