Introduction
The circadian clock with a 24-hour period is an essential biological and
behavioral system that persists in plants, animals, and humans and
regulates a variety of processes, including the cell cycle, body
temperature, immunity, heartbeat, basal metabolism, blood pressure,
hormone secretion, sleep-wake cycle, feeding, and glucose homeostasis
(1). The system is coordinated with environmental stimuli such as food
intake, light, and temperature (2). In humans, the circadian rhythm
consists of two components: the brain clock in the anterior
hypothalamus, supra chiasmatic nucleus (SCN), and the peripheral clock
in the individual cells (3, 4, 5, 6). The brain clock regulates the
peripheral clock of cells and functions as a pacemaker (3, 4, 5, 6).
Cellular clocks have autonomous rhythms and answer to intermittent
signals from the SCN (3, 4, 5, 6). Additionally, circadian pathway genes
control the circadian rhythm (7, 8).
In 1917, 1978, 1997, and 2001, the clock genes were reported for the
first time in the fruit fly Drosophila , the fungusNeurospora , the rat, and finally the human, respectively
(9). In 2017, the Nobel prize was awarded to scientists who
discovered critical molecular mechanisms that control the circadian
rhythm (10, 11). The Per (period homolog)1, 2, 3, Clock ,BMall , and Cry (cryptochrome) 1,2 genes and their products
constitute a
transcription-translation
feedback loop (TTFL) associated with the circadian rhythm (12). During
the day, Clock and BMall interact to initiate the
transcription of the Cry and Per genes (12). TheCry and Per proteins are subsequently linked in the
cytoplasm (12). This complex migrates to the nucleus and inhibitsBMall and Cry gene-mediated transcription (12). TheCry-Per complex is destroyed at night, and the cycle begins again
(12).
Cancer is a significant cause of death worldwide (13). Cancer incidence
has increased due to aging, changes in associated risk factors, and
socioeconomic developments (14). Furthermore, some mutations in DNA
replication and exogenous or endogenous DNA damage are associated with
cancer (15, 16). Several studies showed that disruption in circadian
rhythm results in metabolic syndrome, endocrine disorders, and cancer
(17). In circadian patterns, individuals are typically classified as
morning or evening types (18). Morning types wake up early and function
better in the morning (18). Evening types stay up late and perform best
at night (18). Dysregulation of circadian rhythms in humans is
associated with different cancers such as hepatocellular carcinoma (19),
colon (20), ovarian cancers (21), prostate (22), and lung (23).
Consequently, the proper function of clock proteins and circadian rhythm
plays a crucial role in cancer prevention and treatment (24). In this
study, we aimed to assess the circadian rhythm types using MEQ in cancer
patients.