1 Department of Neuroscience, Institute of Molecular and Cellular Medicine, Okayama University Medical School, Okayama 700- 8558, Japan. 2 Address correspondence to: Ken-ichi Tanaka, PhD, Department of Neuroscience, Institute of Molecular and Cellular Medicine, Okayama University Medical School, 2-5-1 Shikatacho, Okayama 700-8558, Japan. Tel: (+ 81) 86-235-7410; Fax: (+ 81) 86-235- 7412; E-mail: kntanaka@cc.okayama-u.ac.jp Molecular Mechanism in Activation of Glutathione System by Ropinirole, a Selective Dopamine D2 Agonist Ken-ichi Tanaka, 1,2 Ikuko Miyazaki, 1 Naoko Fujita, 1 Md Emdadul Haque, 1 Masato Asanuma, 1 and Norio Ogawa 1 (Accepted October 6, 2000) We have previously reported that ropinirole, a non-ergot dopamine agonist, has neuroprotec- tive effects against 6-hydroxydopamine in mice based on in vivo antioxidant properties such as the glutathione (GSH)-activating effect. In the present study, we determined that the ef- fects of ropinirole on the level of expression of GSH-related enzyme mRNA, these enzymes were shown to regulate GSH contents in the brain. This study focused on the mechanism of GSH enhancement by ropinirole. Striatal GSH contents were significantly increased by 7-day daily administration of ropinirole. Furthermore, the expression levels of γ-glutamylcysteine synthetase (γ-GCS), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione S-transferase (GST) mRNA increased following daily injections of ropinirole for 7 days. In addition, ropinirole treatment for 7 days suppressed auto-oxidation in mouse striatal homo- genates, in contrast to the vehicle treatment. In conclusion, ropinirole was able to suppress auto-oxidation, most probably by increasing GSH levels due to an increase of GSH synthe- sis. In addition, it is likely that auto-oxidation was also suppressed by the activation of GSH- regulating enzymes such as GPx, GR, and GST in the mouse striatum. Thus, our results indicate that the GSH-activating effect of ropinirole may render this dopamine agonist bene- ficial as a neuroprotective drug. KEY WORDS: Ropinirole; dopamine D2 agonist; non-ergot derivative; glutathione. Neurochemical Research, Vol. 26, No. 1, 2001, pp. 31–36 31 0364-3190/01/0100–0031$19.50/0 © 2001 Plenum Publishing Corporation degenerative diseases. To control harmful oxidative stress, cells have evolved efficient detoxification pathways. Of the various antioxidants in the brain, the glutathione (GSH) system is particularly impor- tant in controlling cellular redox states and is the pri- mary defense mechanism for peroxide removal from the brain (1–3). To minimize free radical production in the brains of patients with PD, reduction of the dose of levodopa and/or concomitant use of antioxidants may be ef- fective (4,5). Dopamine (DA) agonists such as bro- mocriptine, pergolide, cabergoline or ropinirole, are reported to have neuroprotective effects in experimen- tal animal models (6–9). Moreover, there are some re- ports on the possibility of preventive effects of DA agents in the clinical progression of the disease INTRODUCTION It is well known that oxidative stress plays an important role in the pathogenesis and progression of Alzheimers disease, Parkinsons disease (PD), and other neurodegenerative diseases. Therefore, antioxi- dant properties may contribute to the neuroprotective effects of drugs indicated for the control of neuro-