Results from the study, “Smoking is associated with increased disease activity during natalizumab treatment in multiple sclerosis,” were recently published in the Multiple Sclerosis Journal.
Multiple sclerosis (MS) is a multifactorial disease associated with both genetic and environmental risk factors. Smoking, in particular, has been linked to numerous aspects of MS, including its development and progression.
In a previous study, the research team looked at how smoking influences the relapse rate in RRMS patients being treated with interferon (IFN)-beta. From more than 800 patients, they found that smoking one pack per day (about 20 cigarettes) essentially interfered with the positive effect of the IFN-beta treatment and increased the relapse rate by 27%.
The researchers then questioned whether the same was true for other treatments.
Tysabri, developed by Biogen, is a monoclonal antibody that targets the alpha-4 integrin protein. By interfering with this molecule, the therapy prevents white blood cells from moving into the central nervous system, suppressing the immune reaction that contributes to MS symptoms.
In the study, 355 Tysabri-treated RRMS patients from the Danish Multiple Sclerosis Centre were assessed. To gather information on smoking habits and body mass index, the patients filled out a 100-question survey. Data was collected between the start of the treatment and a two-year follow-up visit.
Results showed that smoking one pack of cigarettes per day increases the relapse rate by 38% in RRMS patients on Tysabri.
This increase in relapse rate takes into account both sex and age at the start of treatment, since age can affect the relapse rate. For example, an increase in age by one year raises the number of relapses by 2%.
The researchers also looked at the relationship between smoking and the presence of two immune-related alleles: HLA-DRB1*15:01 and HLA-A*02:01. Previous studies showed that HLADRB1*15:01 is associated with an increased risk of developing MS, while HLA-A*02:01 is linked to a decreased risk.
Although previous studies reported a link between smoking and these two alleles in MS patients, the current study did not find an association between smoking and carrying either of these alleles.
Based on the results, the researchers concluded that smoking significantly increases the relapse rate in RRMS patients receiving Tysabri.
According to the team, the results “add important information that hopefully will sharpen the focus on the overall harmful effects of smoking in MS patients.”