Tobacco smoke could increase pain in people with a spinal cord injury, according to a recent study.

A neurotoxin called acrolein found in tobacco smoke that is thought to increase pain in people with spinal cord injury has now been shown to accumulate in mice exposed to the equivalent of 12 cigarettes daily over a short time period.

Researchers from Purdue University found that the pain being exacerbated by acrolein could be reduced by the drug hydralazine, which has been approved by the U.S. Food and Drug Administration for hypertension. The drug has been shown to be effective in reducing acrolein levels in research animals, and researchers are working to develop a low-dose version for that purpose in humans.

"This is the first animal study demonstrating that an acute short term of weeks of smoking could also cause acrolein to accumulate in urine and more importantly in spinal cord tissue, a part of central nervous system known to be vulnerable to acrolein," Riyi Shi, a professor in Purdue University's Department of Basic Medical Sciences, College of Veterinary Medicine, and Weldon School of Biomedical Engineering, said in a statement.

For the study, mice were exposed to a level of acrolein equivalent to 12 cigarettes per day over three weeks. Previous research has focused on acrolein accumulation in the respiratory system but not in the bloodstream and spinal cord. It is known that acrolein is accumulated in urine in human smokers after years of smoking.

Acrolein is produced within the body after nerve cells are damaged. In spinal cord injury and in multiple sclerosis, the myelin insulation surrounding nerve cells is destroyed and the nerve fibers themselves are damaged by acrolein. The toxin acrolein also is found in air pollutants including tobacco smoke and auto exhaust.

"It is already known that smoking can increase pain for people with spinal cord injury and worsen the condition of multiple sclerosis, but we don't know exactly why," Shi said. "I am saying that acrolein might be the key culprit here and that inhaled acrolein could intensify multiple sclerosis and increase pain sensation."

The findings are detailed in the journal Neuroscience Bulletin.