EFFECTS OF NICOTINE ON HYDROXYL FREE-RADICAL FORMATION IN-VITRO AND ON MPTP-INDUCED NEUROTOXICITY IN-VIVO

Parkinson's disease (PD) is one of the most frequent disorders of the basal ganglia. From epidemiological studies there is a controversial d iscussion on the question whether tobacco smoking is correlated with a decreased incidence of PD. The present study aimed to elucidate the r ole of nicotine and its potential neuroprotective effects in a rodent model of PD. These effects may be related to an altered hydroxyl radic al formation; this possibility was studied in vitro. Nicotine and alph a-phenyl-N-tert-butyl nitrone (PBN) were examined in a cell-free in vi tro Fenton system (Fe3+/EDTA + H2O2) for their radical scavenging prop erties using the salicylate trapping method. Salicylic acid (0.5 mM) w as incubated in the presence and absence of nicotine or PEN and the ma in products of the reaction of hydroxyl radicals with salicylic acid, namely 2,3- and 2,5-dihydroxybenzoic acid, were immediately determined using HPLC in combination with electrochemical detection. Nicotine an d PEN were both able to significantly reduce hydroxyl radical levels a t concentrations of 1, 2.5 and 5 mM. Interestingly, at 5 mM nicotine w as able to reduce hydroxyl radical levels significantly more than the radical scavenger PEN (5 mM). To investigate the in vivo effects of ni cotine, male C57BL/6 mice were used in the MPTP mouse model of PD. Nic otine (0.1 or 0.4 mg/kg s.c.) was administered twice daily for a perio d of 14 days. On day 8 a single injection of 1-methyl-4-phenyl-1,2,3,6 -tetrahydropyridine (MPTP, 30 mg/kg s.c.) was given as well as an enha nced protocol of nicotine treatment (0.1 or 0.4 mg/kg s.c., 30 min bef ore MPTP and 30, 90, 210, 330, 450, 570 min after MPTP) for a total of seven injections of nicotine. High dosage nicotine treatment signific antly increased the MPTP-induced loss of body weight and resulted in a significantly decreased striatal dopamine content and an increased do pamine turnover in comparison with the MPTP-treated controls at day 15 . However, the lower dosage of nicotine did not significantly alleviat e the MPTP-induced effects? although some parameters showed a slight t endency in this direction. These results demonstrate that in vitro nic otine has radical scavenging properties which might suggest neuroprote ctive effects. In vivo experiments with nicotine, however, showed that a low dosage of nicotine did not alleviate the MPTP-induced dopamine depletion, but a large dosage even enhanced it.