Effect of exposure to the carcinogen 50 ppm 4-nitroquinoline 1-oxide on alveolar bone loss

Abstract

Background: The objective of this study was to analyze the effect of exposure to the carcinogen 4-nitroquinoline 1-oxide (4NQO), with or without experimental periodontitis (EP), on alveolar bone loss (ABL) in rats.

Materials and methods: Male Wistar rats (n = 84) were divided into Group 1: no EP and no exposure to 4NQO; Group 2: exposure to 4NQO (50 ppm) only; Group 3: EP only; and Group 4: after 20 weeks of exposure to 4NQO (50 ppm), EP was induced by placing a silk ligature on the upper right maxillary second molar for 15 days. Macroscopic analysis of the tongue and morphometric analysis of ABL were performed. Kruskal-Wallis and Mann-Whitney U tests were used, and a significance level of P < 0.05 was adopted.

Results: All animals exposed to 4NQO presented macroscopic lesions on the tongue. When considering the side with EP, no statistically significant difference was demonstrated between Groups 3 (median: 0.76; intervals interquartile [IQ]: 0.42-0.45) and 4 (median: 0.78; IQ: 0.70-0.80). In the side without EP, Group 4 (median: 0.51 mm; IQ: 0.45-0.70) presented significantly higher ABL compared to Group 1 (median: 0.41 mm; IQ: 0.38-0.43). Group 3 (median: 0.44; IQ: 0.41-0.47) showed no significant difference when compared to Groups 1 (median: 0.41; IQ: 0.38-0.43) and 2 (median: 0.46; IQ: 0.41-0.54).

Conclusions: It was concluded that higher ABL occurred in the presence of a carcinogen. However, the combination of both 4NQO and EP did not promote higher ABL.

Keywords: Inflammation; mouth neoplasms; periodontal diseases; rats.

Figure 1

A flowchart illustrating the different experimental phases of the study. 4NQO – 4-nitroquinoline 1-oxide

Figure 2

An example of the five measurements conducted for assessing alveolar bone loss in the present study

Figure 3

Macroscopic view of the tongue from an animal not exposed to a carcinogen (a), an animal exposed to 4-nitroquinoline 1-oxide (4NQO) with a less pronounced lesion (b), and an animal exposed to 4NQO with a well-differentiated lesion (c). Histopathological analyses were performed in the tongue and categorized into no alteration, hyperplasia, mild dysplasia, moderate dysplasia, severe dysplasia, carcinoma in situ, well-differentiated carcinoma, moderately differentiated carcinoma, and poorly differentiated carcinoma

Figure 4

Boxplot of alveolar bone loss (in millimeters) on the side without (a) and with experimental periodontitis (EP) (b). Group 1 (control) indicates no EP and no exposure to 4-nitroquinoline 1-oxide (4NQO). Group 2 (4NQO) indicates exposure to 4NQO without EP. Group 3 (EP) indicates EP without exposure to 4NQO. Group 4 (4NQO+EP) indicates 20 weeks of exposure to 4NQO with EP induced for 15 days. *Statistical significance (P < 0.05)