The major green tea polyphenol, (-)-epigallocatechin-3-gallate, induces heme oxygenase in rat neurons and acts as an effective neuroprotective agent against oxidative stress.
BACKGROUND
Oxidative stress induced by hyperglycemia is a key factor in the pathogenesis of diabetic complications, such as neuropathy. Recently, green tea catechins have received much attention, as they can facilitate a number of antioxidative mechanisms and improve glycemic control.


OBJECTIVE
The aim of this study was to investigate the cytoprotective effects of (-)-epigallocatechin-3-gallate (EGCG) against oxidative stress damage in a cell line of rat neurons. The role of heme oxygenase 1 (HO-1) induction by EGCG and the transcriptional mechanisms involved were also evaluated.


METHODS
Immortalized rat neurons (H 19-7) were exposed to various concentrations of EGCG (10-200 microM). After treatments (6 or 24 hours), cells were harvested for the determination of heme oxygenase activity, mRNA levels, and protein expression. Nuclear levels of Nrf2, a transcriptional factor involved in HO-1 activation, were also measured. Neurons were pretreated for 12 hours with EGCG 50 microM or EGCG 50 microM + zinc protoporphyrin IX 10 microM and then exposed for 2 hours to 50 mmicro/mL glucose-oxidase before cell viability was determined.


RESULTS
In cultured neurons, elevated expression of HO-1 mRNA and protein were detected after 6 hours of incubation with 25-100 microM EGCG, and its induction relates with the activation of Nrf2. Interestingly, pre-incubation (12 hours) with EGCG 50 microM resulted in an enhanced cellular resistance to glucose oxidase-mediated oxidative damage; this cytoprotective effect was considerably attenuated by zinc protoporphyrin IX, an inhibitor of heme oxygenase activity.


CONCLUSIONS
In this study, we demonstrated that EGCG, the major green tea catechin, induced HO-1 expression in cultured neurons, possibly by activation of the transcription factor Nrf2, and by this mechanism was able to protect against oxidative stress-induced cell death.
Romeo
Loriana
L
SPES Dipartimento di Scienze per la Salute, Facoltà di Medicina, Università del Molise, via DeSanctis, Campobasso, Italy.
Intrieri
Mariano
M
D'Agata
Velia
V
Mangano
Nunzio Guido
NG
Oriani
Giovannangelo
G
Ontario
Maria Laura
ML
Scapagnini
Giovanni
G
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D028241:Camellia sinensis / Q000737:chemistry*; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology; D005786:Gene Expression Regulation; D051547:Heme Oxygenase-1 / Q000235:genetics / Q000378:metabolism*; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D009474:Neurons / Q000187:drug effects*; D018696:Neuroprotective Agents / Q000494:pharmacology; D018384:Oxidative Stress / Q000187:drug effects*; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D011524:Protoporphyrins; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013662:Tea / Q000737:chemistry
D000975:Antioxidants; D051267:NF-E2-Related Factor 2; D018696:Neuroprotective Agents; D010936:Plant Extracts; D011524:Protoporphyrins; D012333:RNA, Messenger; D013662:Tea; C017803:zinc protoporphyrin; D002392:Catechin; C045651:epigallocatechin gallate; D051547:Heme Oxygenase-1