Anti-Cancer Effects of Green Tea by Either Anti- or Pro- Oxidative Mechanisms.

Tea derived from the leaves and buds of Camellia sinensis (Theaceae) is consumed worldwide. Green tea contains various components with specific health-promoting effects, and is believed to exert protective effects against diseases including cancer, diabetes and hepatitis, as well as obesity. Of the various tea components, the polyphenol catechins have been the subject of extensive investigation and among the catechins, (-)-epigallocatechin gallate has the strongest bioactivity in most cases. Our research group has postulated that hepatocyte nuclear factor-4α, sterol regulatory element-binding proteins, and tumor necrosis factor-α are targets of green tea constituents including (-)-epigallocatechin gallate for their anti-diabetes, anti-obesity, and anti-hepatitis effects, respectively. Published papers were reviewed to determine whether the observed changes in these factors can be correlated with anti-cancer effects of green tea. Two major action mechanisms of (-)-epigallocatechin gallate have been proposed; one associated with its anti-oxidative properties and the other with its pro-oxidative activity. When reactive oxygen species are assumed to be involved, our findings that (-)-epigallocatechin gallate down- regulated hepatocyte nuclear factor-4α, sterol regulatory element-binding proteins, and tumor necrosis factor-α may explain the anti-cancer effect of green tea as well. However, further studies are required to elucidate which determinant directs (-)-epigallocatechin gallate action as an anti-oxidant or a pro-oxidant for favorable activity.

Effect of radical scavenger N-tert-butyl-alpha-phenylnitrone on stroke in a rat model using a telemetric system.

We used malignant stroke-prone spontaneously hypertensive rats (M-SHRSP) as a stroke model to explore the effects of the radical scavenger N-tert-butyl-alpha-phenylnitrone (PBN) on stroke. PBN was administrated in drinking water to M-SHRSP. Circadian rhythms in heart rate, blood pressure, and locomotive activity in M-SHRSP were monitored with a telemetric system, in addition to measurement of water intake and body weight. Stroke-onset was assessed by changes in neurological symptoms, water intake, and body weight. Circadian rhythms were basically the same between PBN-treated and control rats several days after stroke onset. Significant differences were seen in blood pressure, relative weight of brain and water intake, heart rate, and locomotive activity between two groups. As a result, no significant difference in age of stroke onset was seen between PBN-treated and control rats, but PBN-treated rats displayed prolonged mean life spans. PBN might be effective in prolonging life span.

Preventive effects of green tea catechins on spontaneous stroke in rats.

BACKGROUND: Green tea catechins possess potent antioxidative properties and protect against various oxidative diseases. Malignant stroke-prone spontaneously hypertensive rats (M-SHRSP) develop severe hypertension and spontaneous stroke at early ages. We previously reported that ingestion of green tea catechins prevents cerebral ischemic damage in a middle cerebral artery occlusion and reperfusion rat stroke model, in association with increased plasma epigallocatechin-gallate (EGCG) concentrations. In this study, we examined whether tea catechin intake decreases the incidence of spontaneous stroke in M-SHRSP. MATERIAL/METHODS: Male M-SHRSP ingested 0.5% green tea catechin extract (Polyphenon E) in their drinking water beginning at 5 weeks of age, and blood pressure, heart rate, and locomotor activity were continuously monitored from 8 weeks using a telemetry system. Stroke onset was assessed by the appearance of neurologic symptoms, body weight loss, and circadian rhythm disturbances in heart rate, blood pressure, and locomotor activity. RESULTS: Tea catechin ingestion significantly delayed stroke onset by 10 days compared to the control group. Although there was no difference in blood pressure at 10 weeks, the rate of in blood pressure increase in the tea catechin group was significantly smaller than that in the control group. Plasma NO2- and NO3- concentrations increased after stroke in both groups without significant difference between the two groups. Plasma EGCG concentration significantly decreased at post-stroke compared with that of pre-stroke. CONCLUSIONS: Continuous ingestion of green tea catechins from an early age prevented the development of spontaneous stroke in M-SHRSP, probably by inhibiting the further development of high blood pressure at later ages.

Feasibility of simple chitosan sheet as drug delivery carrier.

Chitosan, a biodegradable and biocompatible polysaccharide, is a potentially useful material in various fields. We developed a simple chitosan sheet and examined the possibility of using an adriamycin-containing chitosan sheet as a drug carrier for controlled release. To prepare a carrier consisting only of chitosan, a chitosan suspension was subjected to acid-alkaline treatment, mixed with adriamycin, frozen and freeze-dried. The adriamycin-containing chitosan sheet was inserted into the peritoneal cavity of mice in order to investigate its biodegradation. The appearance of decomposition of chitosan was observed using scanning electron microscopy, and adriamycin in urine and liver was detected for 1 and 2 weeks, respectively. Adriamycin metabolites were detected in plasma for 2 weeks. Furthermore, adriamycin remained in the chitosan sheet without being metabolized after 2 months. These results suggested that the chitosan sheet prepared in this study might improve therapeutic efficacy in topical lesions as a carrier of sustained-release drugs.

Nitric oxide and effect of a radical scavenger N-tert-butyl-alpha-phenylnitrone on stroke in a rat model.

To characterize the role of nitric oxide (NO) in stroke, NO was measured using an in vivo microdialysis technique and electron spin resonance spectrometry in malignant stroke-prone spontaneously hypertensive rats (M-SHRSP), stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY). The brain dialysate NO level was higher in SHRSP than in WKY. NO was not detected in M-SHRSP hippocampus microdialysate after stroke except after the administration of N-tert-butyl-alpha-phenylnitrone (PBN). In addition, very little NO was generated in M-SHRSP brain tissue with hemorrhage. These data demonstrate an association between NO and stroke in M-SHRSP. Further, PBN administration results in maintenance of NO levels after stroke in M-SHRSP.

ESR characterization of a novel spin-trapping agent, 15N-labeled N-tert-butyl-alpha-phenylnitrone, as a nitric oxide donor.

We previously found that one of the pharmacological effects of N-tert-butyl-alpha-phenylnitrone (PBN) is the release of nitric oxide (NO) under oxidative conditions. However, to confirm this hypothesis in vivo, NO released from PBN must be distinguished from NO produced in biological systems, and therefore we undertook the synthesis of PBN using labeled 15N to identify its corresponding 15NO in vivo. The properties were examined with an ESR spectrometer. To synthesize 15N-PBN, the starting material, ammonium-15N chloride, was converted to 2-amino-15N-2-methylpropane, oxidized to 2-methyl-2-nitropropane-15N, and finally reacted with benzaldehyde to give 15N-PBN. The final product was purified by repeated sublimation. With ferrous sulfate-methyl glucamine dithiocarbamate complex, Fe (MGD)2, as a trapping agent to measure the NO levels of 15N-PBN or 14N-PBN in vitro, the peak intensity of 15NO[Fe(MGD)2] was over 50% stronger than that of 14NO[Fe(MGD)2], and that 15NO and 14NO had the corresponding two-and three line hyperfine structures due to their nuclear spin quantum numbers. Subsequently, the ESR spectrum of 15NO derived from 15N-PBN was significantly different than that of lipopolysaccharide (LPS)-induced NO, which was derived from biological cells, and therefore we have demonstrated the possibility to distinguish 15NO from PBN and 14NO generated from cells. These results suggested that 15N-PBN is a useful molecule, not only as a spin-trapping agent, but also as an NO donor to explore the pharmacological mechanisms of PBN in vivo.

Protective effect of spin trap agent, N-tert-butyl-alpha-phenylnitrone on hyperoxia-induced oxidative stress and its potential as a nitric oxide donor.

We have previously suggested that the spin trap agent, N-tert-butyl-alpha-phenylnitrone (PBN) can function not only as an antioxidant but also as a nitric oxide (NO) donor. To characterize the pharmacological activities of PBN against oxidative damage, we examined the effect of PBN on NO generation under hyperoxic conditions. The formation of NO in mice exposed to 95% oxygen was determined using a NOx analyzer and electron spin resonance (ESR). Levels of NOx, an oxidative product of NO, increased in the blood of mice under these conditions. However, the increase was returned to a normal level by the NOS (nitric oxide synthase) inhibitor, L-NMMA, indicating that the NO was formed via a biosynthetic pathway. In addition, ESR spectra of the liver and brain of control and experimental mice that were measured using Fe(DETC)2 as an NO trap reagent showed strong ESR signals from NO complexes in the livers of mice exposed to 95% oxygen. When examining the effect of PBN in mice, PBN reduced the NOx formation in the blood under the same hyperoxic conditions. In addition, the ESR intensity of the NO complex was weaker in the PBN-treated mice than in the non-treated mice, showing that PBN possess anti-inflammatory properties. However, under a normal atmosphere, NOx and ESR analyses showed that NO levels increased in PBN-treated mice but not in control mice. These findings suggested that PBN functions as an NO donor under specific physiological conditions. PBN appears to protect against hyperoxia-induced NO toxicity by anti-inflammatory action rather than by serving as an NO donor.