Protective effects of nicotine against aminochrome-induced toxicity in substantia nigra derived cells: implications for Parkinson's disease

Abstract

Parkinson's disease is a debilitating progressive neurodegenerative disorder that results from the loss of or damage to dopaminergic cells containing neuromelanin in the substantia nigra (SN). The underlying neurodegenerative mechanism(s), however, remain elusive. Aminochrome, the precursor of neuromelanin is an endogenous substance capable of inducing selective neurotoxicity to dopaminergic neurons in SN. Nicotine, on the other hand, may offer protective effects against dopaminergic cell damage induced by various neurotoxins including MPTP and salsolinol. In this study, we sought to determine whether nicotine may also protect against aminochrome-induced toxicity in SN derived RCSN-3 cells. Exposure of RCSN-3 cells to a combination of aminochrome (50 μM) and dicoumarol (50 μM) for 48 h induced approximately 70 % cell death. Pretreatment with nicotine, dose-dependently blocked this toxicity. The effects of nicotine in turn were dose-dependently blocked by mecamylamine, a non-selective nicotinic receptor antagonist. These results suggest involvement of nicotinic receptors in protective effects of nicotine against aminochrome-induced toxicity and provide further evidence for possible therapeutic effects of nicotine or nicotinic agonists in Parkinson's disease.

Fig. 1

Effects for various concentrations of aminochrome (AM) (20 and 50 μM) with and without dicoumarol (DIC) (50 μM) on % cell death in RCSN-3 cells. Cells were incubated for 48 h. Values are mean ± SEM of five independent experiments *p < 0.05, **p < 0.01 compared to control, ^†p < 0.05, ^††p < 0.01 compared to AM only

Fig. 2

Effects for various concentrations of nicotine (NIC) (1–20 μM) on toxicity induced by the combination of aminochrome (AM, 50 μM) and dicoumarol (DIC, 50 μM) in RCSN-3 cells. Nicotine was added 1 h before the combination of AM + DIC. Cells were incubated for 48 h. Values are mean ± SEM of five independent experiments *p < 0.05, **p < 0.01 compared to control, ^†p < 0.05, ^††p < 0.01 compared to AM + DIC

Fig. 3

Effects for various concentrations of mecamylamine (MEC, 5-100 μM) on RCSN-3 cells. Cells were incubated for 48 h. Values are mean ± SEM of five independent experiments. *p < 0.05, **p < 0.01 compared to control

Fig. 4

Effects for various concentrations of mecamylamine (MEC, 5 and 10 μM) on protective effects of nicotine (NIC) (20 μM) on toxicity induced by the combination of aminochrome (AM, 50 μM)) and dicoumarol (DIC, 50 μM) in RCSN-3 cells. Mecamylamine was added 1 h before nicotine which was added 1 h before the combination of AM + DIC. Cells were incubated for 48 h. Values are mean ± SEM of five independent experiments **p < 0.01 compared to control, ^†p < 0.05, ^††p < 0.01 compared to AM + DIC ^#p < 0.05, ^##p < 0.01 compared to AM + DIC + NIC