Green tea extracts may stop Parkinson's: study

The study, conducted in rats, looked at the effects of green tea polyphenols (GTP) on inhibiting the death of neurons induced by the neurotoxin 6-hydroxydopamine (6-OHDA).

The results are published in the journal Biological Psychiatry .

Parkinson's disease is a degenerative condition affecting movement and balance in more than one million Americans each year, a figure expected to rise due to ageing populations.

According to background information in the article, the disease is caused by an unrelenting process of cell death affecting the neurons containing pigmented dopamine (DA).

Researchers, led by Baolu Zhao from the Institute of Biophysics, Academia Sinica, Beijing, randomly assigned male Sprague-Dawley rats to one of six groups: control-fed only; control-fed plus 6-OHDA; GTP (150 mg/kg/day) plus 6-OHDA; GTP (450 mg/kg/day) plus 6-OHDA; GTP (150 mg/kg/day) only; GTP (450 mg/kg/day) only.

Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent.

Oolong tea is semi-fermented tea and is somewhere between green and black tea.

The four primary polyphenols found in fresh tealeaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).

The mix used in this new study contained 50 per cent EGCG, 22 per cent ECG, 18 per cent EGC, and 10 per cent EC (Sichuan Full-green Biology Technology).

Zhao and co-workers report that the green tea polyphenols protected against the toxic effects of 6-OHDA, with the higher dose producing a higher protective effect.

Most notable, were the inhibition of increases in ROS and NO levels, and subsequent lipid peroxidation.

"This study shows that, in vivo, GTP partially protected dopaminergic neurons (3.7 times more remaining neuron in GTP-treated than vehicle-treated animals) from 6-OHDA-induced cell death through ROS-NO pathway," wrote the researchers.

Commenting independently on the study, John Krystal, editor of Biological Psychiatry and affiliated with both Yale University School of Medicine and the VA Connecticut Healthcare System said: "If green tea consumption can be shown to have meaningful neuroprotective actions in patients, this would be an extremely important advance."

He added a note of caution however, saying that many health-related benefits have been reported for a wide variety of naturally-occurring substances with many being contradicted by subsequent clinical trials.

This is the case with St. John's Wort and Ginko Biloba, he said.

"Thus, it is extremely important to identify the putative neuroprotective mechanisms in animal models, as Guo and colleagues have begun to do for Parkinson's disease," said Krystal.

Source: Biological Psychiatry (Elsevier) 15 December 2007, Volume 62, Issue 12, Pages 1353-1362 "Protective Effects of Green Tea Polyphenols in the 6-OHDA Rat Model of Parkinson's Disease Through Inhibition of ROS-NO Pathway" Authors: Shuhong Guo, J. Yan, T. Yang, X. Yang, E. Bezard and B. Zhao