White matter integrity in young smokers: a tract-based spatial statistics study

Abstract

Previous diffusion tensor imaging (DTI) studies revealed contradictory effects of smoking on fractional anisotropy (FA). Multiple DTI-derived indices may help to deduce the pathophysiological type of white matter (WM) changes and provide more specific biomarkers of WM neuropathology in the whole brain of young smokers. Twenty-three young smokers and 22 age-, education- and gender-matched healthy non-smoking controls participated in this study. Tract-based spatial statistics was employed to investigate the WM microstructure in young smokers by integrating multiple indices, including FA, mean diffusivity (MD), radial diffusivity (RD) and axial diffusivity (AD). Compared with healthy non-smoking controls, young smokers showed significantly increased FA with increased AD and decreased RD in several brain regions, while no difference in MD was observed. Specifically, the overlapped WM regions with increased FA, increased AD and decreased RD were found in the right posterior limb of the internal capsule, the right external capsule and the right superior corona radiata. Additionally, average FA and RD values in the WM regions mentioned earlier were significantly correlated with pack-years and Fagerström Test for Nicotine Dependence, while no correlation in AD was found. The WM tracts with increased FA may be more associated with RD, rather than AD in young smokers. We suggested that WM properties of several fibres in young smokers may be the biomarker as the cumulative effect and severity of nicotine dependence.

White matter development and tobacco smoking in young adults: A systematic review with recommendations for future research

“…Typically, the loss of myelin is associated with greater radial diffusion, or water diffusion perpendicular to the axon, and less axial diffusion, or water diffusion parallel to the axon; reviewed in (Mori and Zhang, 2006). Thus, findings from Yu et al (2015) of decreased radial diffusivity accompanied by increased axial diffusivity within tracts including the internal and external capsules are consistent with the notion of an increase in myelination among adolescent smokers (although more direct evidence is needed to support this hypothesis). However, as this study only included male smokers, additional studies assessing multiple indices of white matter in both male and female adolescent and young adult smokers are needed to confirm and extend these findings.…”

“…Thus, increased FA among adolescent/young adult smokers may be a consequence of exposure to nicotine. Consistent with this interpretation, positive associations between pack years and FA values within the genu (Jacobsen et al, 2007) and corona radiata (Yu et al, 2015) were reported among adolescent/young adult smokers. In contrast to this, negative associations between FTND scores and FA values within the anterior cingulum (Huang et al, 2013) and corona radiata (Yu et al, 2015) were also reported.…”

“…Consistent with this interpretation, positive associations between pack years and FA values within the genu (Jacobsen et al, 2007) and corona radiata (Yu et al, 2015) were reported among adolescent/young adult smokers. In contrast to this, negative associations between FTND scores and FA values within the anterior cingulum (Huang et al, 2013) and corona radiata (Yu et al, 2015) were also reported. Thus, one hypothesis is that lower FA values might be a vulnerability factor for physical dependence during adolescence/young adulthood whereas higher FA values might emerge as a function of exposure to nicotine during this time.…”

“…Two of the five studies identified included assessment of MD; however, findings were not consistent across studies, with one study reporting decreased MD (van Ewijk et al, 2015) and the other no differences (Yu et al, 2015). At the microstructural level, decreased MD has been associated with increases in intracellular fluid content, or cytotoxic edema, due to excess water content within the myelinated axon; reviewed in (Lin et al, 2015).…”

“…All identified studies reported increases in FA among adolescent/young adult smokers in comparison to control participants, and these were most frequently reported in regions of the corpus callosum (genu, body and splenium), internal capsules and superior longitudinal fasciculus (Jacobsen et al, 2007; Liao et al, 2011; van Ewijk et al, 2015; Yu et al, 2015). Taken together, these data suggest that tobacco smoking among adolescents and young adults is associated with increases in white-matter fiber coherence or ‘integrity’, insofar as these may be inferred from FA values.…”