Investigations concerning the impact of consumption of hot beverages on acute cytotoxic and genotoxic effects in oral mucosa cells

Abstract

Consumption of very hot beverages and foods increases the incidence of oral and esophageal cancer but the mechanisms are not known and the critical temperature is not well defined. We realized a study with exfoliated cells from the oral cavity of individuals (n = 73) that live in an area in Iran which has the highest incidence of EC worldwide. Consumption of beverages at very high temperatures is a characteristic feature of this population. We analyzed biomarkers which are (i) indicative for genetic instability (micronuclei that are formed as a consequence of chromosomal damage, nuclear buds which are a consequence of gene amplifications and binucleated cells which reflect mitotic disturbances), (ii) markers that reflect cytotoxic effects (condensed chromatin, karyorrhectic, karyolitic and pyknotic cells), (iii) furthermore, we determined the number of basal cells which is indicative for the regenerative capacity of the buccal mucosa. The impact of the drinking temperature on the frequencies of these parameters was monitored with thermometers. We found no evidence for induction of genetic damage but an increase of the cytotoxic effects with the temperature was evident. This effect was paralleled by an increase of the cell division rate of the mucosa which was observed when the temperature exceeded 60 °C. Our findings indicate that cancer in the upper digestive tract in drinkers of very hot beverages is not caused by damage of the genetic material but by an increase of the cell division rate as a consequence of cytotoxic effects which take place at temperatures over 60 °C. It is known from earlier experiments with rodents that increased cell divisions lead to tumor promotion in the esophagus. Our findings provide a mechanistic explanation and indicate that increased cancer risks can be expected when the drinking temperature of beverages exceeds 60 °C.

Figure 1

Morphology of different anomalies which are scored in MN-cytome experiments with buccal cells. For a detailed description of the characteristics of the different anomalies and scoring criteria see Refs.^,.

Figure 2

(A–E) Estimated number (and 95% confidence intervals) of cellular anomalies and basal cells as a function of the average temperature of beverages. Estimation by Poisson regression with restricted cubic splines (KR karyorrhexis, KL karyolysis, CC condensed chromatin).

Figure 3

Schematic representation of the study design. More than 200 individuals were asked if they are willing to participate in the study; only those who were healthy non-smokers and consumed ≥ 3 cups of hot beverage daily over a period of 21 days were eligible. The participants filled in questionnaires concerning their lifestyle and demographic data. The temperature of the consumed beverages was measured twice with thermometers (at the start and end of consumption period). Mouth cells were collected with cytobrushes, fixed and stained and evaluated microscopically. We sampled in total 82 individuals, only slides from 73 subjects contained a sufficient number of cells for cytome analyses.