Circadian disruption induced by light-at-night accelerates aging and promotes tumorigenesis in rats

Abstract

We evaluated the effect of various light/dark regimens on the survival, life span and tumorigenesis in rats. Two hundred eight male and 203 females LIO rats were subdivided into 4 groups and kept at various light/dark regimens: standard 12:12 light/dark (LD); natural lighting of the North-West of Russia (NL); constant light (LL), and constant darkness (DD) since the age of 25 days until natural death. We found that exposure to NL and LL regimens accelerated development of metabolic syndrome and spontaneous tumorigenesis, shortened life span both in male and females rats as compared to the standard LD regimen. We conclude that circadian disruption induced by light-at-night accelerates aging and promotes tumorigenesis in rats. This observation supports the conclusion of the International Agency Research on Cancer that shift-work that involves circadian disruption is probably carcinogenic to humans.

Keywords: life span; light-at-night; rats; tumorigenesis.

Figure 1.

Dynamics of the coefficient of homeostatic stability (CHS) in female (A) and male (B) rats maintained at various light regimens. ^ The difference with the relevant parameter in the group LD is significant, р<0,05; * The difference with the parameter at the age of 3 months in the same group is significant, р<0,05 (Wilcoxon-Mann-Whytney test).

Figure 2.

Age-related dynamics of incidence of irregular estrous cycles in rats maintained at various light/dark regimens. Ordinate, number of rats with irregular estrous cycles (%). The difference with the relevant parameter in the group LD is significant, р<0.05.

Figure 3.. Effect of the exposure to various light regimens on survival and tumorigenesis in rats.

(A) - survival, males; (B)- survival- females; (C) - total tumor incidence, males; (D) - total tumor incidence, females; (E) - malignant tumor incidence, males; (F) - malignant tumorincidence, females.