Association of the Cytotoxic Effects of Waterpipe and Cigarette Smoke Extract with Relative Telomere Length (RTL) in Breast Cancer Cell Lines

Abstract

Background: Breast cancer ranks the first leading cause of cancer worldwide in 2020 as declared by the International Agency for Research on Cancer (IARC). Breast cancer development and progression involve a wide range of genetic alterations including shortening or lengthening of telomere length. Telomeres maintain the genetic integrity hence cellular stability as they are important in protecting the end of chromosomes from fusion, and in avoiding the loss of coding nucleotides during each DNA replication. Any replication problem can result in shortening of telomere during each cell division reaching a critical length and causing the cell to become senescent. There is currently no comparative literature on telomerase expression and telomere length of waterpipe and cigarette smoking, and this is an important area of research given the strong carcinogenic effects of waterpipe smoke exposure and its increasing use worldwide. Methods: The aim of this study is to identify the change in relative telomere length associated with the cytotoxic potential of waterpipe smoke in breast cancer cell lines in comparison to cigarette smoke. We exposed MCF-7 and MDAMB-231 cells to cigarette and waterpipe smoke extracts and tested cytotoxicity with MTT assay for choice of sub-toxic concentrations, trypan blue assay for cell counting, RNA and protein isolation for telomerase expression and activity respectively and DNA for relative telomere length. Results: Exposure of breast cancer cells to acute subtoxic waterpipe and cigarette smoke extract showed a decrease in telomerase activity that was compensated by an increase in hTERT telomerase expression to potentially escape the proliferation barriers in cell senescence from G0/G1 cell cycle arrest resulting in enhanced carcinogenesis. Conclusion: Our results went a step further in elucidating a telomerase-linked mechanism between telomerase activity and its rate-limiting determinant hTERT expression. Further studies on cell cycle, genotoxicity, invasion, and migration are required to explain our results, in addition to exposing cells to chronic subtoxic concentrations that would mimic the lifetime exposure of smokers in-vivo. The proposed approach may pave the way for the use of RTL as a biological marker for toxicity of cigarette and waterpipe in breast cancer.