Green tea (Camellia sinensis) catechin profiles in plasma and urine following single dosing and regular ingestion of green tea are not clear. We performed a placebo-controlled intervention study with sixteen healthy volunteers to determine changes in total and free catechins after a single dose and following 1 week of twice-daily green tea. Blood and urine samples were collected before (fasting) and after (60 and 120 min for blood; 90 and 180 min for urine) drinking 200 ml of 1·5 % (w/v) green tea or water (n 8 each), and fasting samples were again collected after 7 d of 150 ml of 1 % (w/v) supplemental green tea or water twice daily. After a 4-week washout, subjects were crossed onto the other treatment and procedures repeated. Plasma results at 1 h post-ingestion showed elevated (P, 0·05) mean epigallocatechin gallate (EGCG; 310 (SD 117) nmol/l; all in free form), epigallocatechin (EGC; 192 (SD 67) nmol/l; 30 % free) and epicatechin gallate (ECG; 134 (SD 51) nmol/l; 75 % free). Fasting plasma after 7 d of regular intake showed increased (P,0·05) EGCG (80 v. 15 nmol/l at baseline) and ECG (120 v. 40 nmol/l), with $ 90 % of both in their conjugated forms. Total EGC was , 10 nmol/l. Post-ingestion conjugation and renal loss of EGC and epicatechin were rapid and high, but were negligible for EGCG and ECG. In the green tea consumed, the content was EGCG . EGC . ECG, and the acute plasma response mirrored this. However, after chronic consumption there was almost no EGC found in fasting plasma, some EGCG was present, but a rather high level of ECG was maintained.Key words: Green tea: Catechins: Polyphenols: Epigallocatechin gallate: Bioavailability: Biotransformation: Antioxidants Green tea (Camellia sinensis) is reported to have various beneficial effects on health (1 -3) . Green tea is rich (35 % of dry weight) in catechins, a family of polyphenolic flavon-3-ols, and these are the putative bioactive agents (2 -4) . The major catechin (about 60 -70 %) in green tea is epigallocatechin gallate (EGCG), but there are also substantial amounts of epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC) (2 -4) . In vitro studies have demonstrated the powerful antioxidant properties of catechins, particularly EGCG (3 -6) , and human studies have shown that the plasma total antioxidant capacity increases shortly after the ingestion of green tea (3,5,7) . However, poor gastrointestinal absorption, rapid phase II metabolism and urinary excretion of conjugated catechins severely limits their bioavailability and, thereby, their biological effects (4,5,8 -10) . Including the absorption (assessed by their urinary excretion) of ring fission catechin metabolites produced from colonic bacteria increases 'catechin' bioavailability to about 40 % (ranging from ,3 to 100 %), but interindividual differences in urinary concentrations of these metabolites are very large, and their physiological relevance is currently unknown (9 -15) .

Objectives: This is a narrative review, investigating the antioxidant properties of drugs used in the management of diabetes, and discusses whether these antioxidant effects contribute to, confound, or conceal the effects of antioxidant therapy. Methods: A systematic search for articles reporting trials, or observational studies on the antioxidant effect of drugs used in the treatment of diabetes in humans or animals was performed using Web of Science, PubMed, and Ovid. Data were extracted, including data on a number of subjects, type of treatment (and duration) received, and primary and secondary outcomes. The primary outcomes were reporting on changes in biomarkers of antioxidants concentrations and secondary outcomes were reporting on changes in biomarkers of oxidative stress. Results: Diabetes Mellitus is a disease characterized by increased oxidative stress. It is often accompanied by a spectrum of other metabolic disturbances, including elevated plasma lipids, elevated uric acid, hypertension, endothelial dysfunction, and central obesity. This review shows evidence that some of the drugs in diabetes management have both in vivo and in vitro antioxidant properties through mechanisms such as scavenging free radicals and upregulating antioxidant gene expression. Conclusion: Pharmaceutical agents used in the treatment of type 2 diabetes has been shown to exert an antioxidant effect..

Genoprotection by low-dose green tea could be due to direct antioxidant protection by green tea polyphenols, or to H2O2-independent signalling pathways.

The comet assay measures DNA damage in individual cells (usually lymphocytes) and is widely used in biomonitoring studies. Lymphocytes are harvested and are usually cryopreserved for batch testing. We investigated cell loss during harvesting, cryopreservation, thawing, and washing of human peripheral lymphocytes and compared DNA damage, using the Fpg-assisted comet assay for oxidation-induced DNA lesions, in freshly harvested cells and cells that were thawed and tested after cryopreservation of 2-3 days and 4 weeks. Lymphocyte numbers were measured in fresh venous blood and after the steps of harvesting, cryopreservation, and washing. Results showed that >50% of lymphocytes in whole blood were harvested, but ∼60% were lost during washing. Loss during washing was not different (P>0.05) between fresh cells and cells thawed and washed after 2-3 days or 4 weeks cryopreservation. No change in DNA damage was seen after cryopreservation and thawing: mean (SD) % DNA in comet tail was 11.2 (1.53) in freshly harvested cells, 12.9 (1.39) in 2-3 days cryopreserved cells, and 12.9 (2.0) in cells tested after 4 weeks cryopreservation (P>0.05). Results indicate that there is no predominant loss of more highly damaged cells during cryopreservation and thawing and there is no induction of oxidation-induced DNA lesions in cryopreserved cells stored for up to 4 weeks.

Regular intake of green tea (Camellia sinensis) lowers DNA damage in humans, but molecular mechanisms of genoprotection are not clear. Protection could be via direct antioxidant effects of tea catechins, but, paradoxically, catechins have pro-oxidant activity in vitro, and it is hypothesized that mechanisms relate to redox-sensitive cytoprotective adaptations. We investigated this hypothesis, focusing particularly on effects on the DNA repair enzyme human oxoguanine glycosylase 1 (hOGG1), and heme oxygenase-1, a protein that has antioxidant and anti-inflammatory effects. A randomized, placebo-controlled, human supplementation study of crossover design was performed. Subjects (n = 16) took a single dose (200 mL of 1.5%, w/v) and 7-days of (2 × 200 mL 1%, w/v per day) green tea (with water as control treatment). Lymphocytic DNA damage was ∼30% (p < 0.001) lower at 60 and 120 min after the single dose and in fasting samples collected after 7-day tea supplementation. Lymphocytic hOGG1 activity was higher (p < 0.0001) at 60 and 120 min after tea ingestion. Significant increases (p < 0.0005) were seen in hOGG1 activity and heme oxygenase-1 after 7 days. Results indicate that molecular triggering of redox-sensitive cytoprotective adaptations and posttranslational changes affecting hOGG1 occur in vivo in response to both a single dose and regular intake of green tea, and contribute to the observed genoprotective effects of green tea.

Tea polyphenols (catechins) have various reported properties that may benefit health and lower risk of non-communicable disease. However, their bioavailability is low. There is rapid metabolism and elimination of most absorbed catechins, and they do not accumulate beyond nanomolar amounts in plasma, even with regular intake. There is extensive biotransformation of unabsorbed catechins by colonic microflora, which produces ring scission products that, if included, increase bioavailability from an average of <4% to around 40%. Strategies exist to increase bioavailability, such as taking tea catechins in the fasting state, or taking more concentrated, purified, stable or bioaccessible formulations of catechins. However, catechins demonstrate pro-oxidant activity under certain conditions, and administration of high levels induces toxic effects on liver and kidney. In humans catechins are generally well tolerated at up to 400 mg/day, but even this dose can cause gastrointestinal upset and in some people induces hepatic toxicity. Furthermore, catechins bind iron and high doses can interfere with iron absorption, and catechins ingestion affects pharmacokinetics and action of some drugs used to treat hypertension and cardiovascular disease. Therefore, strategies to overcome low bioavailability of catechins must be viewed with caution, and very high doses should be avoided. In this article, absorption, metabolism and bioavailability of green tea catechins, in particular epigallocatechin gallate, are reviewed, focusing mainly on human data. Issues of potential toxicity of catechins are examined, and a recommendation in regard to 'safe' intake is given.

No abstract

No abstract