Lopinavir/ritonavir treatments severely affected the growth of gingival epithelium when the drug was present throughout the growth period. To the best of our knowledge, the correlation between lopinavir/ritonavir levels in blood serum and in oral tissues has not been widely studied. However, earlier studies showed that drug levels were almost equal in blood serum and in saliva [23–25]. Therefore, we assumed that the blood levels of

lopinavir/ritonavir signaling pathway would be the same as in the saliva. As the oral cavity is directly exposed to saliva, we expect that the intracellular concentration of the drug in the oral cavity tissues would be equal or close to its Cmax (9.8 μg/mL). In the present study, at even lower concentrations

of lopinavir/ritonavir (3 and 6 μg/mL), the growth of gingival epithelium was severely inhibited. To examine the HIF inhibitor effect of lopinavir/ritonavir on epithelium integrity using TEM, we treated raft cultures at day 8. TEM observations clearly illustrated that lopinavir/ritonavir treatments affected cell-to-cell packing by directly or indirectly reducing desmosome adhesiveness. As desmosomes are intercellular junctions that provide strong adhesion between cells and also give mechanical strength to tissues [19], the results of our study suggest that lopinavir/ritonavir treatments affected gingival epithelium integrity. The results of the present study are consistent with those of our previous study in which amprenavir treatments also affected epithelial growth and integrity [20]. However, the adverse impact of lopinavir/ritonavir on tissue growth and integrity was more severe compared with amprenavir treatments. Our results Sucrase support

previous findings that indicated that the use of antiretroviral drugs, including protease inhibitors, resulted in the development of oral complications [6,8–11]. These observations suggest the possibility that the oral epithelium in HIV-infected patients exposed to HAART develops drug-induced abnormalities in the cellular and molecular biology of the tissue which give rise to oral complications. However, our raft culture model is an in vitro model in which the study of growth kinetics is limited to a maximum of 20 days. In contrast, patients undergoing drug therapy have potentially been exposed to these drugs for a numbers of years. As a result, our raft culture system provides a snapshot of the drug effects during a limited growth period. However, the effects of the drugs are representative of the adverse oral effects reported in patients undergoing antiviral therapy. Different cytokeratins are differentially expressed during development and differentiation and vary in different types of epithelia [18,32]. Normally, cytokeratins 5 and 14 are expressed only in the proliferative basal layer of gingival stratified epithelia [28–30].