No data are available on the concentration of ZDV in the oral cavity. However, we expect that in the oral cavity the concentration of

the drug should be close to or lower than its Cmax (2 μg/mL). This assumption and previous data from studies investigating the effects of protease inhibitors on gingival tissues led us to use the concentrations indicated. The growth of the gingival epithelium was inhibited when the drug ZDV, an NRTI, was added at day 0 and was present throughout the growth period. In the present study, ZDV, even at lower concentrations (0.5 and 1 μg/mL), below the Cmax, affected the growth of the gingival epithelium, disrupting its proliferation and stratification status. These results support previous findings that indicated that the use of antiretroviral drugs resulted in the development of oral complications, especially with long-term use [2, 3, 5, 7, 9]. Our observations GSK126 cell line suggest that the oral epithelium in HIV-positive patients exposed to HAART, including ZDV, experiences drug-induced abnormalities

in the molecular and cellular biology of the tissue, which give rise to these oral complications. Epithelial tissues express different pairs of cytokeratin proteins depending on HKI-272 chemical structure the epithelial cell type and stage of differentiation [17, 18]. During the process of terminal differentiation, keratinocytes lose their ability to proliferate and migrate from the basal layer to the superficial layers while Fluorouracil concentration undergoing a coordinated series of morphological, biochemical and genetic changes. The terminal differentiated

cell is a flattened dead cell that consists of a network of cytokeratin filaments surrounded by an insoluble envelope of heavily cross-linked protein [37]. When cells make the commitment to terminally differentiate, one of the changes to occur is a switch in cytokeratin gene expression. Expression of cytokeratins 5 and 14 is shut off and that of cytokeratin 1 and 10 is turned on [38]. Cytokeratin 10 is indicative of terminal differentiation and is expressed in the suprabasal layer of keratinized epithelia. It has also been reported that cytokeratin 10 protects the epithelium from trauma and damage [31]. To examine the effect of ZDV on the proliferation and differentiation of oral keratinocytes, we treated raft cultures at day 0 and at day 8. Normally, gingival stratified epithelia express the cytokeratin pair of cytokeratins 5 and 14 only in the proliferative basal layer; however, the cytokeratin pair is maintained in all layers of tissue [28, 30]. In this study, cytokeratins 5 and 14 were detected in all layers of the tissue in untreated samples. Application of ZDV decreased the amount of cytokeratin 5 present in tissues (Fig. 3). The amount of cytokeratin 14 present in tissues was also reduced (data not shown).