Taken together, these results suggest that COX-2 expression is significantly up-regulated in OSF tissues from areca quid chewers and arecoline may among other constituents be responsible for the enhanced COX-2 expression in vivo. The regulation of COX-2 expression induced by arecoline is critically dependent on the cellular GSH concentration.

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Growth characteristics and lysyl oxidase activity of fibroblasts derived from human normal mucosa (NM) and oral submucous fibrosis (OSF) associated with betel nut chewing were compared in cell cultures. The growth rates of cultured cells were identified by plating 5 x 10(5) cells/35 mm culture dish (Day 0) and every 24 hours cell proliferation was determined by quantifying the cell number (using a hemocytometer). The third to seventh passages were used. A medium without serum but supplemented with 5 mg/ml bovine serum albumin was substituted for the original medium at the subconfluent period and cultured for an additional 24 h. The medium was collected and used for assays of protein content and lysyl oxidase activity. Lysyl oxidase activity was assayed with [4,5-3H]--lysine labelled purified chick--embryo aorta elastin substrate. After incubation for 10 h at 37 degrees C, the enzyme activity was measured from 3HHO (tritiated water) separated by ultrafiltration using Amicon C-10 micro-concentrators. The results showed the mean doubling time of OSF fibroblasts was 3.2 days and of NM fibroblasts was 3.6 days. NM fibroblasts became confluent at day 6 as determined by cell number, while OSF fibroblasts were confluent by Day 5. Furthermore, the immunoenzymatic assay for BrdUrd incorporation revealed that OSF fibroblasts proliferate significantly faster than NM fibroblasts under standard culture conditions. Both total protein content (10.84 +/- 1.15 mg/ml) and lysyl oxidase activity (3558.6 +/- 345.5 cpm/10(6) cell) in OSF fibroblasts were greater than in NM fibroblasts (6.35 +/- 0.96 mg/ml and 2436.0 +/- 352.6 cpm/10(6) cell). The results of this study provide evidence that fibroblasts derived from oral submucous fibrosis (OSF) tissue and normal mucosa (NM), although similar in many respects, exhibit specific differences in proliferation rates and lysyl oxidase activity. Moreover, collagen deposition in OSF tissue may, at least in part, be ascribed to increased lysyl oxidase activity.

Oral submucous fibrosis (OSF), a chronic oral mucosal condition commonly found in south Asians, is a disorder characterized by a quantitative as well as a qualitative alteration of collagen deposition within the subepithelial layer of the oral mucosa. Since degradation of collagen by fibroblast phagocytosis is an important pathway for physiological remodelling of soft connective tissues, we have investigated phagocytosis of collagen‐ and fibronectin‐coated latex beads by fibroblast cultures with an in vitro model system. Coated fluorescent latex beads were incubated with human oral mucosa fibroblasts and the fluorescence associated with internalized beads was measured by flow cytometry. Cells from normal tissues that had been incubated with beads for 16 h contained a mean of 75% collagen phagocytic cells and 70% fibronectin phagocytic cells; however, about 15% and 10% of phagocytic cells individually contained more than twice the mean number of beads per cell. In contrast, cells from OSF tissues exhibited a 40% reduction of the proportions of collagen phagocytic cells (mean=35%) and a 48% decrease of the proportions of fibronectin phagocytic cells (mean=22%), none of the cells having a high number of beads as compared to normal fibroblasts. OSF lesions appear to contain fibroblasts with marked deficiencies in collagen and fibronectin phagocytosis. To investigate if inhibition of phagocytosis could be demonstrated in vitro, normal fibroblast cultures were incubated with areca nut alkaloids (arecoline, arecaidine). The cultures had a dose‐dependent reduction in the proportions of phagocytic cells. On the other hand, corticosteroid used in the treatment of OSF exhibited a dose‐dependent enhancement in the proportion of phagocytic cells. Therefore, our hypothesis for OSF, although over‐simplified, is that betel nut alkaloids (arecoline, arecaidine) inhibit fibroblast phagocytosis and this provides a mechanism for the development of OSF. The benefit of a local intralesional injection of corticosteroid is also possibly, at least in part, through an enhancement of fibroblast collagen phagocytosis.