Khat Induces Abnormal Differentiation of Reconstituted Human Oral Mucosa

Introduction: Khat is pyschostimulant drug that is widely used in Eastern Africa and the Middle East. Khat use has been associated with various pathological conditions of the oral mucosa including increased keratinisation and oral cancer.

Objectives: This study investigated the effects of an extract of khat on differentiation of normal human buccal keratinocytes grown in three dimensional organotypic cultures on top of collagen matrices containing normal human buccal fibroblasts.

Methods: Differentiation was assessed by examination of haematoxylin-eosin stained samples under light microscopy, assay for the activity of transglutaminase enzymes and western blot analysis of specific markers.

Results: Samples exposed to the extract of khat had a reduced total epithelial thickness, but with an increase in the proportion of the superficial layer relative to the total thickness. Khat treated samples also had increased activity of transglutaminase enzymes compared to untreated controls. The levels of involucrin and cytokeratin 10, specific markers of differentiation for keratinized oral epithelia which are low in native buccal and in vitro reconstituted epithelia were elevated in khat-exposed samples, while the levels of fillaggrin and cytokeratin 13, specific markers of differentiation in non-keratinized oral epithelia were low. Further investigation showed that the levels of p38 protein were also higher in khat-exposed cultures compared to controls.

Conclusions: Taken together, these findings show that khat induces abnormal differentiation of human oral keratinocytes in a reconstituted buccal mucosa, and that this could be mediated through p38 MAP kinase signalling. Whether this explains the hyperkeratosis reported in the oral mucosa of khat users should be elucidated in future studies.

Funding: The study was supported partly by the L. Meltzer's College Fund, Gades Legat and the Dental Faculty, University of Bergen.