Molecular and cellular aspects of smoking on fracture healing: a comparison of two models

Objective: The detrimental effect of smoking on the fracture healing processis well documented clinically. However, the effect of smoking on the fracturemicroenvironment is ill defined. Mesenchymal stem cells (MSCs) play the keyrole in fracture healing. The aim is, therefore, to study the effects of smoking atthe cellular level by comparing ex vivo MSCs (smoker versus non-smoker) withcells in an in vitro model (smoke-treated cells versus untreated cells).Methods: Fracture haematomas were collected during operative fixation fromnon-smoking (n=11) and smoking (n=6) patients who sustained tibial fracture.The haematoma was explanted and maintained in culture (37°C humidified0·05 CO2) incubator. Cells were characterised via immunofluorescence andimmunophenotyping using known MSC-antibody markers (CD29, CD44,CD105 and CD166). Ex-vivo model: MSCs were counted after 5 days usingflow cytometer; proliferation rates were compared between non-smoker andsmokers. In-vitro model: Cigarette smoke extract (CSE) was prepared (accordingto Bernhard, 2004). Cells from non-smoking patients were divided into twogroups and cultured as before. One group was treated with the CSE, whichwas equilibrated to 20 cigarettes per day smoker and the other left untreated ascontrol. Cell populations were counted and compared after 5 days.Results: Ex-vivo model: Proliferation rates were reduced by 41·19% (SEM±7·78%) in those cells extracted from smokers’ MSCs. In-vitro model: Cellcounting showed a reduction in the rate of proliferation of cells in the smoketreated group by 40·8% (SEM± 1·9%).Conclusion: Fracture haematoma MSCs, when exposed to tobacco smoke;proliferate at similar decreased rate in both ex vivo and in vitro models