Khat induces G1‐phase arrest and increased expression of stress‐sensitive p53 and p16 proteins in normal human oral keratinocytes and fibroblasts

Abstract

Khat is a psychostimulant plant used by over 10 million people daily, mainly in eastern Africa and the Middle East. Previous studies have suggested an association between khat use and oral lesions such as hyperkeratosis and oral cancer. This study investigated the effects of an extract of khat on primary normal human oral keratinocytes (NOK) and normal human oral fibroblasts (NOF). Low (sublethal) concentrations of khat inhibited the proliferation of both cell types in a dose-dependent and time-dependent manner. Both NOK and NOF treated with khat accumulated in the G1-phase of the cell cycle and showed increased expression of the stress-sensitive p53 protein after 24 h. Normal human oral keratinocytes showed a profound increase in p16(INK4A) (p16) after 24 h and showed morphological changes suggesting cell differentiation. Normal human oral fibroblasts showed growth inhibition and increased expression of p21(WAF1/CIP1) (p21) within 24 h. The concentrations of khat tested in this study were within the range of those found in the oral cavity of khat chewers. The results show that stress induced by khat modulates the cell cycle in oral keratinocytes and fibroblasts. It is further speculated whether khat could have similar effects in vivo, especially in keratinocytes.

Distinct single cell signal transduction signatures in leukocyte subsets stimulated with khat extract, amphetamine-like cathinone, cathine or norephedrine

“…Based on cathinone, cathine and norephedrine concentrations in the khat-extract, the experimental dilutions should be comparative to local concentrations of khat constituents in vivo during khat chewing (Table 1) [26]. The impact on signal transduction proteins and stress sensors in T-lymphocytes, B-lymphocytes, natural killer (NK) cells and monocytes was assessed using modification-specific antibodies and flow cytometric analyses (Figure 1A).…”

“…Our studies have shown that exposure of various cell types (i.e. leukemic cell lines, normal oral keratinocytes and fibroblasts, normal peripheral leukocytes) to khat-extract in vitro affects various proteins involved in cell death, cell stress, cell cycle regulation, differentiation and cell signaling [26,30,31,33,37]. …”

Qat Chewing and Risk of Potentially Malignant and Malignant Oral Disorders: A Systematic Review

“…31 An organic Qat extract was shown to induce tumor suppressor proteins and G1 cell cycle arrest in normal oral fibroblast and keratinocytes in vitro. 32 Furthermore, the study showed that Qat induced premature differentiation and keratinization in oral keratinocytes grown in co-cultures with normal fibroblasts, possibly through signaling of p38 MAP kinase. 32 When exposed to a higher concentration of Qat the oral fibroblasts and keratinocytes underwent programmed cell death in a process involving reactive oxygen species.…”

“…32 Furthermore, the study showed that Qat induced premature differentiation and keratinization in oral keratinocytes grown in co-cultures with normal fibroblasts, possibly through signaling of p38 MAP kinase. 32 When exposed to a higher concentration of Qat the oral fibroblasts and keratinocytes underwent programmed cell death in a process involving reactive oxygen species. 33 Moreover, the study also found that oxidative stress can occur in oral cells exposed to Qat.…”

Qat and its health effects

“…47,48 A more recent paper investigated the effects of qat on human oral keratinocytes and human oral fi broblasts in respect to changes present at the cell cycle level. 49 The results showed qat to have a strong inhibitory effect on the growth of these two cell types, with increased expression of tumour suppressor genes involving senescence related to differentiation. Whether these changes are mirrored in vivo is yet to be determined.…”