[The promoter effects of sodium butyrate on the malignant transformation of the immortalized esophageal epithelium induced by human papillomavirus].

Objective: Study on the promoter effects of sodium butyrate in high or low dosages on carcinogenesis process, based on the immortalization of human fetal esophageal epithelium induced by human papillomavirus (HPV) 18E(6)E(7) genes.

Methods: The immortalized esophageal epithelium SHEE was treated with high concentration of the sodium butyrate (80 mmol/L) and then with low concentration (5 mmol/L) for 8 weeks respectively. The cells were cultured continuously without sodium butyrate for 14 weeks. The morphology, proliferation and apoptosis of the cells were studied by phase contrast microscopy, immunohistochemistry and flow cytometry. The dead and the viable cells were assayed by fluorescent microscopy with Hoechst 33342 and Propidium iodide staining. Tumorigenesis of the cells was assessed by soft agar colony formation and by transplantation of cells into nude mice and SCID mice.

Results: When cells were exposed to high concentration of sodium butyrate, cell death was increased leaving few live cells. When cells were cultured in the medium with low concentration of sodium butyrate, the first proliferative stage appeared. Removal of the butyrate caused the cell to enter a crisis stage with a long doubling time resembling senescent cells. After the crisis stage, the cells progressed to the second proliferation stage with continuous replication and atypical hyperplasia. At the end of the second proliferative stage, carcinogenesis of the cells appeared with large colonies in soft-agar and tumor formation in transplanted SCID mice and nude mice.

Conclusions: The malignant change of the immortalized epithelium by the effects of sodium butyrate is the consequence of a two-stage mortality mechanism: cells death by butyrate cytotoxicity and cell crisis by abrogation of sodium butyrate. These data reveal that in high dosage, sodium butyrate induces cell death and in low dosage, it induces cell proliferation, which emphasizes the importance of butyrate as a promotor of carcinogenesis.