Dimitrios Stagos

Chemoprevention of liver cancer by plant polyphenols

Primary liver cancer or hepatocellular carcinoma (HCC) is one of the most frequent tumors representing the fifth commonest malignancy worldwide and the third cause of mortality from cancer. Currently, the treatments for HCC are not so effective and new strategies are needed for its fight. Chemoprevention, the use of natural or synthetic chemical agents to reverse, suppress or prevent carcinogenesis is considered an important way for confronting HCC. Many of the chemopreventive agents are phytochemicals, namely non-nutritive plant chemicals with protective or disease preventive properties. In this review, we focus on plant polyphenols, one of the most important classes of phytochemicals, their chemopreventive properties against HCC and discuss the molecular mechanisms accounting for this activity.

Correlation of total polyphenolic content with antioxidant and antibacterial activity of 24 extracts from Greek domestic Lamiaceae species.

Lamiaceae family species are considered important because of their use in folk medicine, culinary and flavouring throughout the world. Their interesting bioactivities are attributed mainly to essential oils, polyphenols and terpenes. However, there are only few studies about polyphenolic extracts from Lamiaceae plants. Thus, 24 polyphenolic extracts from three Lamiaceae genera, Salvia, Mentha and Sideritis, collected in Greece were examined for antioxidant and antibacterial activity in correlation with their polyphenolic content. The results showed that the tested polyphenolic extracts had strong free radical scavenging activity against DPPH· and ABTS(+) radicals and protected from hydroxyl and peroxyl radical-induced DNA damage. Moreover, five extracts inhibited Staphylococcus aureus growth. Furthermore, the results showed that the total polyphenolic content is not correlated with the above activities, although this relation was different within each plant genus. This is the first study regarding the antioxidant and antibacterial activity of Salvia pomifera ssp. calycina, S. pomifera ssp. pomifera, Mentha microphylla and Sideritis raeseri ssp. attica species, and one of the few concerning protection from DNA damage and antibacterial activity of polyphenolic extracts from the rest of the tested species.

Assessment of polyphenolic content, antioxidant activity, protection against ROS-induced DNA damage and anticancer activity of Vitis vinifera stem extracts.

Grape extracts and wine have been studied widely due to their beneficial effects on human health. However, there are only few studies from grape stems extracts. Therefore, the main objective of the present study was the assessment in stem extracts from Greek Vitis vinifera varieties of the total polyphenolic content (TPC), the identification of the polyphenols present in them, and the evaluation of their antioxidant activity, protection against ROS-induced DNA damage and inhibition of liver (HepG2) and cervical (HeLa) cancer cell growth. The range of the TPC in grape stem extracts was from 345 to 584 mg GAE/g dry weight. Moreover, stem extracts contained different classes of polyphenols as flavonols, flavanols, procyanidins, phenolic acids and stilbenes. In DPPH and ABTS assays, the IC50 values of the stem extracts had an average of 7.8 ± 2.8 and 5.4 ± 2.6 μg/mL respectively. Also, all stem extracts inhibited OH- and ROO-induced DNA damage dose dependent with average IC50 values of 478 ± 217 and 1.15 ± 0.85 μg/mL respectively. Furthermore, stem extracts inhibited at low concentrations the growth of HepG2 and HeLa cancer cells with average IC50 values of 50 ± 12 and 32 ± 16 μg/mL respectively. The above activities of grape stem extracts were comparable to those of seed extracts.

Pomegranate juice consumption increases GSH levels and reduces lipid and protein oxidation in human blood.

The aim of the present study was the assessment of the antioxidant effects of pomegranate juice (PJ) consumption in humans. Thus, 14 healthy volunteers consumed PJ daily for a period of 15days and the changes of oxidative stress markers in their blood were assessed at four different time points, immediately before the experiment (T1), after 15days of juice administration (T2), one (T3) and three weeks (T4) after the interruption of PJ administration. The markers studied were total antioxidant capacity (TAC), levels of malondialdehyde (MDA), and protein carbonyls (CARB) measured in plasma, as well as reduced glutathione (GSH), and catalase activity (CAT) measured in erythrocytes. The MDA was reduced by 24.4% at T3 and CARB were reduced by 19.6% and 17.7% at T2 and T3, respectively, supporting the evidence that PJ consumption enhances the antioxidant status in humans by decreasing lipid peroxidation and protein oxidation. Moreover, GSH levels were significantly increased (22.6%) at T2, indicating that PJ consumption improves the antioxidant mechanisms in erythrocytes by increasing GSH levels. Finally, it was shown that even a week after stopping PJ consumption some of its beneficial effects on antioxidant status still remained in the organism.

The Antioxidant Effects of a Polyphenol-Rich Grape Pomace Extract In Vitro Do Not Correspond In Vivo Using Exercise as an Oxidant Stimulus

Fruits, such as grapes, are essential food of the Mediterranean diet. Grape extracts have potent antioxidant and chemopreventive properties in vitro. Numerous studies have examined the effects of plant extract administration on redox status at rest in animals and humans but their results are controversial. However, there are no studies comparing the in vitro and in vivo effects of plant extracts on oxidative stress using exercise as an oxidant stimulus. Thus, the aim of this study was to investigate whether a polyphenol-rich grape pomace extract of the Vitis vinifera species possesses in vitro antioxidant properties and to examine whether these properties apply in an in vivo model at rest and during exercise. Our findings indicate that the tested extract exhibits potent in vitro antioxidant properties because it scavenges the DPPH• and ABTS•+ radicals and inhibits DNA damage induced by peroxyl and hydroxyl radicals. Administration of the extract in rats generally induced oxidative stress at rest and after exercise whereas exercise performance was not affected. Our findings suggest that the grape pomace extract does not behave with the same way in vitro and in vivo.

Anti-inflammatory effects of a special carbohydrate-whey protein cake after exhaustive cycling in humans.

Intense exercise induces increased levels of pro-inflammatory and anti-inflammatory cytokines. Thus, the purpose of this study was to examine the effects of a special cake (consisting of carbohydrate to whey protein 3.5:1) vs. an isocaloric carbohydrate cake on inflammatory markers after exhaustive cycling in humans. Nine subjects received either the experimental or placebo cake in a counterbalanced fashion using a crossover, double-blind, repeated-measures design. They performed one trial involving a 2h exercise on a cycle ergometer at 60-65% VO2max followed by a 4h recovery and then a second trial involving an 1h exercise at 60-65% VO2max which was increased at 95% VO2max. Blood samples were collected pre-exercise, 30 min and 4h post-exercise, post-time Trial and 48 h post-time Trial. Cakes were consumed immediately post-exercise and every 1h for the next 3h. The results showed that consumption of the experimental cake reduced significantly (p<0.05), 4h post-exercise, the pro-inflammatory protein levels IL-6 and CRP compared to the control group by 50% and 46% respectively. Moreover, in the experimental cake group, the level of the anti-inflammatory cytokine IL-10 was higher by 118%, 4h post-exercise, compared to the control group but not statistically significant.

Application of a new oxidation-reduction potential assessment method in strenuous exercise-induced oxidative stress

Abstract Objectives The aim of the study was to test a novel method for assessing oxidative stress, the RedoxSYS™ diagnostic system, a holistic, fast, minimally invasive, and requiring small sample volume method, that measures two parameters, the static (sORP) and the capacity (cORP) oxidation-reduction potential. Methods The redox status of 14 athletes participating in a mountain marathon race was assessed. Redox status in blood obtained 1 day before the race and immediately after the race was assessed using the RedoxSYS diagnostic system as well as conventional oxidative stress markers such as glutathione levels (GSH), catalase activity (CAT), thiobarbituric acid reactive substances (TBARS), protein carbonyls (CARB), and total antioxidant activity. Results The results showed that after the race, the sORP was increased significantly by 7% indicating oxidative stress induction, while cORP was decreased by 14.6% but not significantly. Moreover, the conventional oxidative stress markers GSH and CAT were decreased significantly by 13.1 and 23.4%, respectively, while TBARS and CARB were increased significantly by 26.1 and 15.6%, respectively, after the race indicating oxidative stress induction. Discussion The present study demonstrated for the first time that the RedoxSYS diagnostic system can be used for evaluating the exercise-induced oxidative stress in athletes.

Biochemical and biological assessment of the inhibitory potency of extracts from vinification byproducts of Vitis vinifera extracts against glycogen phosphorylase

The inhibitory potency of thirteen polyphenolic extracts obtained from vinification byproducts of Greek varieties of Vitis vinifera against glycogen phosphorylase (GP) has been studied by kinetic experiments. GP is an enzyme involved in glucose homeostasis and a molecular target for the discovery of new hypoglycemic agents. Studies have shown that all extracts display significant inhibitory potency for GP in vitro with IC50 values in the range of low μg/mL. X-ray crystallographic analysis of GP crystals soaked with two of these extracts revealed that the most active ingredient is quercetin which binds at novel binding site, distinct from the other known sites of the enzyme. One of the most potent of the studied extracts had also a moderate effect on glycogenolysis in the cellular lever with an IC50 value of 17.35 μg/mL. These results highlight the importance of natural resources in the quest for the discovery of new hypoglycemic agents, while at the same time they can serve as the starting point for their exploitation for antidiabetic usage and the development of novel biofunctional foods.

Assessment of Eccentric Exercise-Induced Oxidative Stress Using Oxidation-Reduction Potential Markers

The aim of the present study was to investigate the use of static (sORP) and capacity ORP (cORP) oxidation-reduction potential markers as measured by the RedoxSYS Diagnostic System in plasma, for assessing eccentric exercise-induced oxidative stress. Nineteen volunteers performed eccentric exercise with the knee extensors. Blood was collected before, immediately after exercise, and 24, 48, and 72 h after exercise. Moreover, common redox biomarkers were measured, which were protein carbonyls, thiobarbituric acid-reactive substances, total antioxidant capacity in plasma, and catalase activity and glutathione levels in erythrocytes. When the participants were examined as one group, there were not significant differences in any marker after exercise. However, in 11 participants there was a high increase in cORP after exercise, while in 8 participants there was a high decrease. Thus, the participants were divided in low cORP group exhibiting significant decrease in cORP after exercise and in high cORP group exhibiting significant increase. Moreover, only in the low cORP group there was a significant increase in lipid peroxidation after exercise suggesting induction of oxidative stress. The results suggested that high decreases in cORP values after exercise may indicate induction of oxidative stress by eccentric exercise, while high increases in cORP values after exercise may indicate no existence of oxidative stress.

Polyphenolic composition of grape stem extracts affects antioxidant activity in endothelial and muscle cells

The aim of the present study was the assessment of the antioxidant effects of polyphenolic extracts derived from the stems of three Greek grape varieties (Moshomayro, Mavrotragano and Mandilaria) in endothelial (EA.hy926) and muscle (C2C12) cells. We also investigated the effects of the polyphenolic composition on the antioxidant effects of the grape stem extracts. For this purpose, the endothelial and muscle cells were treated with low non-cytotoxic concentrations of the extracts for 24 h in order to assess the effects of the extracts on cellular redox status using oxidative stress biomarkers. The oxidative stress markers were thiobarbituric acid reactive substances (TBARS), protein carbonyl (CARB) levels, reactive oxygen species (ROS) levels and glutathione (GSH) levels. The results revealed that treatment of the EA.hy926 cells with Mandilaria extract significantly decreased the TBARS levels by 14.8% and the CARB levels by 25.9 %, while it increased the GSH levels by 15.8% compared to the controls. Moreover, treatment of the EA.hy926 cells with Mavrotragano extract significantly increased the GSH levels by 20.2%, while it significantly decreased the TBARS and CARB levels by 12.5% and 16.6%, respectively. Treatment of the C2C12 cells with Mandilaria extract significantly decreased the TBARS levels by 47.3 %, the CARB levels by 39.0 % and the ROS levels by 21.8%, while it increased the GSH levels by 22.6% compared to the controls. Moreover, treatment of the C2C12 cells with Mavrotragano significantly decreased the TBARS, CARB and ROS levels by 36.2%, 35.9% and 16.5%, respectively. In conclusion, to the best of our knowledgel, our results demonstrate for the first time that treatment with grape stem extracts at low concentrations improves the redox status of endothelial and muscle cells. Thus, grape stem extracts may be used for developing antioxidant food supplements or biofunctional foods. However, it was also found that the polyphenolic composition of grape stem extracts affects their antioxidant capacity. For example, the results suggested that trans-resveratrol, gallic acid, (+)-catechin, ferulic acid, caffeic acid, quercetin, coumaric acid and kaempferol may be essential for the antioxidant activity of grape stem extracts.