Washington, March 4 : US researchers have identified a second ingredient in cigarette smoke that delays bone healing after fractures.
A team of experts at the University of Rochester Medical Center had earlier shown in a 2005 study that nicotine delays bone growth by influencing gene expression in the two-step bone healing process-first, when stem cells become cartilage; secondly, when cartilage matures into bone.
In the current study, it has been found that another ingredient in cigarette smoke called the polyaromatic hydrocarbon benzo(a)pyrene (BaP) also slows bone healing, though in a different way.
There is evidence that smoking delays skeletal healing by as much as 60 per cent following fractures, and thereby increases the likelihood of re-injury, chronic pain, and disability.
While experts say that the obvious solution for the smokers is to kick the butt when they get hurt, studies have shown that only 15 per cent can do so.
"Our results provide the first evidence that BaP prevents stem cells from becoming cartilage cells as part of healing," said Dr. Regis J. O'Keefe, chair of the Department of Orthopaedics and Rehabilitation at the Medical Center and a study investigator.
"These findings extend our understanding of the impact of cigarette smoke on a process that is critical to fracture repair. Perhaps down the road we will be able to speed bone healing among smokers in more than one way," he added.
The researcher said that during the study, polymerase chain reaction (PCR), a tech technique that measures gene expression levels, revealed the genetic changes caused by exposure to BaP in mouse stem cells.
He said that the PCR results showed that BaP in cigarette smoke interferes with the expression of a gene called SOX-9, which is required for the transition of stem cells into cartilage cells. Besides BaP was also found to effect the production of type II collagen gene, a fibrous protein framework for cartilage.
"Smoking reduces the rate at which the two sides of a fracture come together. We believe this new research will establish for the first time the mechanisms by which polyaromatic hydrocarbons interfere with the healing process," said Dr. Michael Zuscik, associate professor in the Department of Orthopaedics and Rehabilitation at the Medical Center.
The new finding was presented at the annual meeting of the Orthopaedic Research Society in San Francisco.