Effect of exposure to light‐at‐night on life span and spontaneous carcinogenesis in female CBA mice

Abstract

The effect of constant illumination on the development of spontaneous tumors in female CBA mice was investigated. Fifty female CBA mice starting from the age of 2 months were kept under standard light/dark regimen (12 hr light: 12hr dark; LD) and 50 CBA mice of similar age were kept under constant illumination (24 hr a day, 2,500 Lux, LL). Exposure to the LL regimen decreased food consumption but did not influence body weight, significantly accelerated age-related disturbances in estrous function, and was followed by a significant increase in spontaneous tumor incidence in female CBA mice. Tumor incidence as well as the number of total or malignant tumors was significantly increased in the LL group compared to the LD group (p < 0.001). The incidence of lung adenocarcinomas, leukemias and hepatocarcinomas was 7/50; 6/50 and 4/50 in the LL group and 1/50; 0/50 and 0/50 in the LD group. Mice from the LL groups had shorter life spans then those from the LD group. The data demonstrate, for the first time, that exposure to constant illumination was followed by increases in the incidence of spontaneous lung carcinoma, leukemias and hepatocarcinoma in female CBA mice. Alternation of the day and night circadian cycle is an important regulator of a wide variety of physiological rhythms in organisms. Light exposure at night has been found to be related to a number of serious behavioral and health problems including cancer. In rodents, light-at-night leads to disruption of the ovulatory cycle followed by hyperplastic processes and tumor development in mammary gland, ovaries and uteri. 1,2 A tumor-promoting effect of exposure to the LL regimen was shown on chemical carcinogenesis in the mammary gland of rats. [3][4][5][6] Prolonged light exposure suppresses the night peak of melatonin, the 'hormone of the night.' 7,8 Melatonin is the principal hormone of the pineal gland, the small neuroendocrine gland connected with the brain that mediates information on light from the retina to the organism. 7,8 A significant increase in the risk of breast and colorectal cancers was shown in women who frequently did not sleep during the period of the night, about 1:30 a.m., when melatonin levels are typically the highest. 9 -12 The 'Melatonin hypothesis' suggests reduced pineal melatonin production might increase human breast cancer risk because lower melatonin output would lead to an increase in female sex hormones and stimulate proliferation of breast tissue. 13 Data on the enhancing effect of constant illuminations on spontaneous endometrial carcinogenesis in BDII/Han rats 14 agree with this suggestion. There are data on the promoting effect of the LL regimen on hepatocarcinogenesis induced by N-nitrosodimethylamine (DENA) in rats 15 and on the development of neurogenic and kidney tumors in progeny of rats exposed to N-nitrosomethylurea in utero. 16 We report, for the first time, that exposure to constant illumination increased the incidence of spontaneous lung carcinoma, leukemias and hepatocarcinoma in female CBA mice. MATERIAL AND ME...

Chronic mild stress induces behavioral and physiological changes, and may alter serotonin 1A receptor function, in male and cycling female rats

“…A possibility exists that exposure to continuous overnight illumination produced the observed estrous cycle disruption in the CMS group. However, while previous studies suggest that exposure to constant light lengthens or disrupts the estrous cycle in rodents (Fiske 1941;Maric et al 1965;Cvijić et al 1998), these changes have typically been reported following chronic periods (e.g., from 2 weeks to 3 months) of constant light situations (Ivanišević-Milovanovićc et al 1995;Anisimov et al 2004). In contrast, the brief periods of continuous illumination used in the current protocol (12 h, twice weekly) likely produced minimal, if any, direct effects on the estrous cycle in female rats.…”

Chronically Alternating Light Cycles Increase Breast Cancer Risk in Mice

“…However, the experimental conditions of many of these animal studies were far from the reality of human shift workers. For example, some involved xenografts (addressing tumor growth rather than cancer initiation and/or progression) [4,5], chemically induced tumor models [6,7], or continuous bright light exposure, which can lead to suppression of circadian rhythmicity [8,9]. Here, we have exposed breast cancer-prone p53 R270Hª/+ WAPCre conditional mutant mice (in a FVB genetic background) to chronic CRD by subjecting them to a weekly alternating light-dark (LD) cycle throughout their life.…”

The Role of Transcription Factors Dfoxo, Dsir2 and Hsp70 in Lifespan Alteration of Drosophila Melanogaster in Different Light Conditions

“…2А) достоверно различаются как у самцов, так и у самок (p < 0,001 по критерию Колмогорова-Смирно-ва). У самцов гетерозиготной по гипоморфной аллели гена dSir2 линии Sir2 17 /+, также как и у контрольной линии, в темноте происходило достоверное (p < 0,001) увеличе-ние МеПЖ (на 12 %), времени 90%-й гибели особей (на 17 %, p < 0,004), MRDT, а параметр α уравнения Гомпер-тца в темноте уменьшился на 22 % (p < 0,007 по критерию Хи-квадрат). У самок гетерозиготной линии Sir2 17 /+ в темноте наблюдалось незначительное снижение времени 90 %-гибели особей (на 5 %), MRDT, медиана не измени-лась, а значение параметра α увеличилось на 10 %.…”