question: What is the mechanism of drug-induced gingival overgrowth?
answer: Drug-induced gingival overgrowth (GO) is a frequent and adverse side-effect associated principally with the administration of the immunosuppressive drug cyclosporin A (CsA) and also certain anti-epileptic and anti-hypertensive drugs. It is characterized by a marked increase in the thickness of the epithelial layer and the accumulation of excessive amounts of connective tissue.  Keratinocyte growth factor (KGF), which is a potent epithelial cell mitogen that has been implicated in other hyperplastic conditions could be involved in the molecular pathology of GO. Also, since cathepsin-L deficiency was reported to be associated with thickening of the skin, impaired cathepsin-L activity may play a key role in the establishment of skin and gingival abnormalities seen in I-cell disease. In addition, reduced cathepsin-L activity may play an important role in inducing drug-induced gingival overgrowth. Furthermore, the enhanced proliferation of gingival fibroblasts observed in this disease could be caused at least partly by the effects of the drugs on the cell cycle and cyclin expression in these cells. The increase in cell growth that occurs in drug-induced gingival overgrowth may be mediated by over-expression of cyclin B1.