Evaluation of the Pro-Oxidant and Antioxidant Actions of L-DOPA and Dopamine in Vitro: Implications for Parkinson's Disease

Abstract

The antioxidant and pro-oxidant properties of L-DOPA and dopamine were investigated in vitro. Both compounds inhibited the peroxidation of ox-brain phospholipids, with IC₅₀ values of 8.5 μM for dopamine and 450 μM for L-DOPA. Dopamine and L-DOPA reacted with trichloromethyl peroxyl radicals (CC1₃O₂) with rate constants of 2.1 × 10⁷M¹s^-1 and 1.3 × 10⁷ M^-1s^-1 respectively. The effects of dopamine and L-DOPA on iron ion- dependent hydroxyl radical generation from H₂O₂ were c:mplex. In general, low concentrations stimulated OH formation in the presence of ferric-EDTA and, in the case of L-DOPA, ferric-ADP and ferric citrate chelates. Both compounds also reacted with superoxide radical and hypochlor-ous acid. The products of the reaction with HOCI could still inhibit al-antiproteinase and appear to be 'long lived' chloramine-type oxidizing species. Our results suggest that L-DOPA and dopamine might have a complex mixture of pro- and anti- oxidant effects, which could contribute to tissue damage due to oxidative stress in Parkinson's disease and other neurological disorders.

Key Words:

• Dopamine
• L-DOPA
• Free Radicals
• Antioxidants
• Peroxyl Radicals