Epidemiological studies over the past 50 years have shown a lower incidence of Parkinson’s disease among cigarette smokers. Although this apparent neuroprotective benefit of cigarette smoking has been known for a while, be it due to nicotine or the scores of other chemicals in cigarettes, the mechanism has been poorly understood and the therapeutic implications yet to be taken advantage of in the development of new Parkinson’s disease drugs. The main concern was whether this epidemiological finding was just a coincidence, which although unlikely, had not been clinically verified until the recent years. A new research study conducted at Institut du Cerveau et de la Moelle Épinière, Hôpital de la Salpêtrière, in Paris, France has confirmed the potential benefit of nicotine in Parkinson’s disease by its action on a specific type of receptor on neurons.
Nicotine Effect on Dopamine Release
Nicotine, whether on its own or with other monoamine oxidase inhibitors and yet undiscovered chemicals in cigarette smoke, stimulates the dopaminergic neurons in the brain. These dopamine-producing nerve cells are progressively destroyed in Parkinson’s disease and dopamine is supplemented with the aid of medication like L-dopa. However, the drawback with L-dopa is the side effects and attempting to reduce the dose only worsens the symptoms.
Although previous studies did indicate that the damage to the substantia nigra, the area of the brain most affected in Parkinson’s disease, was limited with nicotine and exacerbated by pesticides and toxins, the exact mechanism and receptor sites for this neuroprotective effect of nicotine were not conclusively verified. It was believed to be those same receptors, alpha-7 nicotine receptors, as was verified by the recent study. These previous studies also put forward the idea that other non-receptor mediated mechanisms may offer protection by suppressing the effect of toxins and altering the activity of the enzyme monoamine oxidase.
Nicotine Receptors on Dopamine Nerves
In the recent study conducted in France, it was found that nicotine spares the gradual loss of these neurons by acting on alpha-7 nicotine receptors. Mice that were genetically engineered without these receptors were shown to be more likely to lose dopaminergic neurons than normal mice with these receptors. These findings were recently published in the FASEB journal (August 2011) and go a long way in opening up possibilities of new drugs that target the alpha-7 nicotine receptors. New generation drugs may be able to prevent Parkinson’s disease in high risk individuals or slow the progression of the disease.
Smoking Benefit in Parkinson’s Disease
The findings of the recent study are promising and offers new hope for Parkinson’s disease like the recent VPS35 genetic mutation discovery which sheds new light on familial Parkinson’s disease. However, this should not encourage every PD patient to take up cigarette smoking. The host of carcinogens (cancer-causing chemicals) in cigarette smoke may be a greater risk to one’s health and lifespan, along with the known cardiovascular implications of cigarette smoking. Nevertheless, the finding does open up some exciting avenues for future development of drugs that can take advantage of the neuroprotective effect of nicotine by now identifying the specific receptors responsible for this benefit.