Effect of dietary vitamin E on spontaneous or nitric oxide donor-induced mutations in a mouse tumor model

Background: Vitamin E, an antioxidant, has been investigated for its effect on cancer incidence in humans, but no firm conclusions about a protective effect can be drawn from these studies. Recently, we reported a statistically significant correlation in the Mutatect mouse tumor model between the number of neutrophils and the frequency of mutation at the hypoxanthine phosphoribosyltransferase (hprt) locus. We have now used this model to investigate vitamin E's effect on the hprt mutation rate, Methods: Mutatect cells were grown in mice as subcutaneous tumors for 2-3 weeks, the tumor cells were recovered, and 6-thioguanine-resistant (i.e., hprt mutant) colonies were scored. Myeloperoxidase activity was used as a measure of neutrophil infiltration. Vitamin E (2 IU/kg body weight) was provided in the diet for 3-4 weeks. In some experiments, glyceryl trinitrate (100 mg/kg body weight) was also administered as a source of nitric oxide. All statistical tests were two-sided. Results: Mouse tumors from the Mutatect MN-11 cell line exhibited a 3.2-fold higher median mutation frequency than the same cells in culture (P < .0001); vitamin E reduced this frequency by 24.9% (P = .01), Mutatect TM-28-derived tumors (which secrete interleukin 8) were heavily infiltrated with neutrophils and had a correspondingly high mutation frequency; in two separate experiments, vitamin E reduced the median mutation frequency by 68.9% (P = .0019) and 84.1% (P = .011) and myeloperoxidase levels by 75.5% (P = .0002) and 75.5% (P = .026), respectively. Glyceryl trinitrate increased the mutation frequency in MN-11 tumors, and vitamin E reduced the median frequency by 61.4% (P = .058), Conclusions: Dietary vitamin E afforded strong protection against both spontaneously arising and nitric oxide-induced mutations. Two separate protective mechanisms by vitamin E may be operating: scavenging of a nitric oxide-related genotoxic species and altering the infiltration of neutrophils into tumors.