Stilbenoids from Rheum undulatum Protect Hepatocytes Against Oxidative Stress Through AMPK Activation

Anti-Stem Cell Property of Pterostilbene in Gastrointestinal Cancer Cells

Pterostilbene (PTE) is a natural sterbenoid contained in blueberries that has an antioxidant effect. In contrast, PTE also generates oxidative stress in cancer cells and provides an antitumor effect. Here, we examined the potential mechanism of this contrasting effect of PTE using three gastrointestinal cancer cell lines, namely CT26, HT29, and MKN74. PTE showed a dose-dependent inhibition of cell proliferation, sphere-forming ability, and stem cell marker expression in all three cell lines. Furthermore, the cells treated with PTE showed an increase in mitochondrial membrane potential and an increase in mitochondrial oxidative stress and lipid peroxide. Upon concurrent treatment with vitamin E, N-acetyl-L-cysteine, and PTE, the PTE-induced mitochondrial oxidative stress and growth inhibition were suppressed. These findings indicate that PTE induces oxidative stress in cancer cells, suppresses stemness, and inhibits proliferation. These antitumor effects of PTE are considered to be useful in cancer treatment.

Stilbenes contribute to the anticancer effects of Rheum undulatum L. through activation of apoptosis

Rheum undulatum L. (R. undulatum) is a medicinal plant used for the treatment of inflammatory diseases in East Asian countries. Numerous stilbenes isolated from R. undulatum have been revealed to possess anticancer effects. The aim of the present study was to evaluate the effect of extracts and compounds isolated from R. undulatum on human gastric cancer cell viability and to elucidate their molecular mechanism of action on the apoptosis pathway. The results demonstrated that aloe-emodin and chrysophanol 1-O-β-D-glucopyranoside, isolated from the methanolic extract of dried rhizomes of R. undulatum, exhibited anti-proliferative effects on the human gastric carcinoma cell line AGS, with IC₅₀ values of 84.66±0.44 and 68.28±0.29 µM, respectively. The percentage of apoptotic cells increased significantly following treatment with each compound at a concentration of 100 µM, compared with that in the non-treated group in the image-based cytometry assay. Western blot analysis revealed that these compounds activated the caspase cascade and inhibited B-cell lymphoma-2, an anti-apoptotic protein.

Pterostilbene inhibits nutrient metabolism and induces apoptosis through AMPK activation in multiple myeloma cells

Multiple myeloma (MM) cells are characterized by an abnormal nutrient metabolism that is distinct from normal plasma cells. Pterostilbene (PTE), a bioactive component of blueberries, has been demonstrated to induce apoptosis in multiple types of cancer cell. The present study evaluated whether PTE treatment affected the survival of MM cells from a metabolic perspective, and the potential mechanisms of this. It was observed that the administration of PTE induced apoptosis, which was mediated by the increased activation of AMP‑activated protein kinase (AMPK). Once activated, AMPK decreased the expression and/or activity of key lipogenic enzymes, including fatty acid synthase and acetyl‑CoA carboxylase. In addition, the activation of AMPK suppressed the downstream substrate, mechanistic target of rapamycin, which dephosphorylated eukaryotic initiation factor 4E‑binding protein 1, leading to a general decrease in mRNA translation. Pre‑treatment with the AMPK inhibitor compound C prior to PTE treatment compromised the anti‑myeloma apoptosis effect, suggesting the critical role of AMPK in mediating PTE‑induced cell toxicity. Consistent results were obtained in vivo. Finally, autophagy was adaptively upregulated subsequent to PTE treatment; the pro‑apoptotic efficacy of PTE was potentiated once autophagic flux was inhibited by 3‑methyladenine. Taken together, these data demonstrated that PTE exerts anti‑tumor effects on MM cells via AMPK‑induced nutrient suppression.

Quantification of desoxyrhapontigenin (4-methoxyresveratrol) in rat plasma by LC-MS/MS: Application to pre-clinical pharmacokinetic study

Desoxyrhapontigenin (DRG, 4-methoxyresveratrol or trans-3,5-dihydroxy-4'-methoxystilbene) is a naturally occurring resveratrol (RES) derivative with a variety of biological activities. To facilitate its further medicinal exploration, a reliable LC-MS/MS method was developed and validated for the quantification of DRG in rat plasma using heavy isotope labelled RES as an internal standard. The ESI was operated in its negative ion mode while DRG and RES were determined by multiple reaction monitoring (MRM) using precursor-to-product ion transitions of m/z 241.1 → 180.8 and m/z 233.0 → 191.0, respectively. This LC-MS/MS method displayed excellent selectivity, sensitivity (LLOQ = 2.5 ng/ml), accuracy (both intra- and interday mean analytical recovery within 100 ± 15%) and precision (both intra- and interday CV < 15%). The mean matrix factors were all within 1.000 ± 0.150 with CV < 15%. The pharmacokinetic profiles of DRG were subsequently examined in Sprague-Dawley rats. Upon intravenous administration (4 or 10 mg/kg), DRG displayed very rapid clearance (Cl = 338 ± 66 or 275 ± 30 ml/min/kg) and short mean residence time (MRT = 12.9 ± 4.7 or 10.4 ± 0.5 min). After oral administration of DRG fully solubilized by 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), the plasma profiles of DRG were highly erratic with a low absolute bioavailability (F < 9.83 ± 5.31%). When DRG was given at a higher dose (50 mg/kg) in suspension form, the F was increased to 24.1 ± 5.6%. The pharmacokinetic comparison among DRG, RES and some of its hydroxyl analogues stilbenes was performed. The information obtained from this study will facilitate further exploration on DRG as well as other RES derivatives.

Structural Modification of Stilbenoids from Acanthopanax leucorrhizus and Their Cytotoxic Activity

A new cis-stilbenoid, 1,9-dihydroxy-10-methoxy-6H-dibenzo[b,f]oxocin-6-one (2) was isolated from the AcOEt extract of the stem barks of Acanthopanax leucorrhizus, along with three known stilbenoids, 9-hydroxy-10-methoxy-6H-dibenzo[b,f]oxocin-6-one (1), 5-O-methyl-(E)-resveratrol 3-O-β-d-glucopyranoside (3), and (E)-resveratrol 3-O-β-d-xylopyranoside (4). Two derivatives (2a and 2b) were synthesized by the structural modification of compound 2, which exhibited certain cytotoxic activities against HT-29 and HeLa cell lines in vitro. All compounds were structurally characterized by comprehensive analysis of their spectroscopic data and comparison with literature information, and evaluated for their cytotoxic activities against three human tumor cell lines (HL-60, HT-29, and HeLa) by the standard MTT assay in vitro. The results showed that derivatives 2a and 2b exhibited strong activities than compounds 2 against HT-29 and HeLa cell lines.

Pterostilbene Inhibits Lipogenic Activity similar to Resveratrol or Caffeine but Differently Modulates Lipolysis in Adipocytes

The anti-obesity effects of resveratrol shown in rodents are not transposed into an efficient therapy of human obesity. Consequently, the search for molecules mimicking or surpassing resveratrol actions is ongoing. The natural phenolic compound pterostilbene exhibits beneficial health effects and has the capacity to limit fat mass in animal models. In this study, we tested whether pterostilbene modulates triacylglycerol accumulation/breakdown. Prolonged exposure to pterostilbene or resveratrol inhibited adipocyte differentiation in 3T3-F442A preadipocytes. Acute effects on lipolysis, antilipolysis and lipogenesis were determined for pterostilbene in mouse adipocytes, and compared with resveratrol. Pterostilbene was also tested on glycerol release and glucose uptake in subcutaneous human adipocytes. Dose-response analyses did not reveal a clear lipolytic effect in both species. The antilipolytic effect of insulin was improved by pterostilbene at 1-10 μM in mouse fat cells only, while at 1 mM, the phenolic compound was antilipolytic in human fat cells in a manner not additive to insulin. Pterostilbene dose-dependently inhibited glucose incorporation into lipids similarly to resveratrol and caffeine. However, only the former did not inhibit insulin-stimulated glucose uptake. Indeed, pterostilbene abolished the insulin lipogenic effect without inhibiting its antilipolytic action and rapid activation of glucose uptake. Pterostilbene therefore exhibits a unique panel of direct interactions with adipocytes that relies on its reported anti-obesity and antidiabetic properties. Copyright © 2017 John Wiley & Sons, Ltd.

ATM/CHK/p53 Pathway Dependent Chemopreventive and Therapeutic Activity on Lung Cancer by Pterostilbene

Among the many stilbenoids found in a variety of berries, resveratrol and pterostilbene are of particular interest given their potential for use in cancer therapeutics and prevention. We purified four stilbenoids from R. undulatum and found that pterostilbene inhibits cancer cell proliferation more efficiently than rhapontigenin, piceatannol and resveratrol. To investigate the underlying mechanism of this superior action of pterostilbene on cancer cells, we utilized a reverse-phase protein array followed by bioinformatic analysis and found that the ATM/CHK pathway is modified by pterostilbene in a lung cancer cell line. Given that ATM/CHK signaling requires p53 for its biological effects, we hypothesized that p53 is required for the anticancer effect of pterostilbene. To test this hypothesis, we used two molecularly defined precancerous human bronchial epithelial cell lines, HBECR and HBECR/p53i, with normal p53 and suppressed p53 expression, respectively, to represent premalignant states of squamous lung carcinogenesis. Pterostilbene inhibited the cell cycle more efficiently in HBECR cells compared to HBECR/p53i cells, suggesting that the presence of p53 is required for the action of pterostilbene. Pterostilbene also activated ATM and CHK1/2, which are upstream of p53, in both cell lines, though pterostilbene-induced senescence was dependent on the presence of p53. Finally, pterostilbene more effectively inhibited p53-dependent cell proliferation compared to the other three stilbenoids. These results strongly support the potential chemopreventive effect of pterostilbene on p53-positive cells during early carcinogenesis.