The circadian clock is an endogenous timekeeper system that controls the daily rhythms of a variety of physiological processes. Accumulating evidence indicates that genetic changes or unhealthy lifestyle can lead to a disruption of circadian homeostasis, which is a risk factor for severe dysfunctions and pathologies including cancer. Cell cycle, proliferation, and cell death are closely intertwined with the circadian clock, and thus disruption of circadian rhythms appears to be linked to cancer development and progression. At the molecular level, the cell cycle machinery and the circadian clocks are controlled by similar mechanisms, including feedback loops of genes and protein products that display periodic activation and repression. Here, we review the circadian rhythmicity of genes associated with the cell cycle, proliferation, and apoptosis, and we highlight the potential connection between these processes, the circadian clock, and neoplastic transformations. Understanding these interconnections might have potential implications for the prevention and therapy of malignant diseases.

Background: Sodium-glucose cotransporter 2 inhibitors (SGLT2i) is the first class of anti-diabetes treatment that reduces mortality and risk for hospitalization due to heart failure. In clinical studies it has been shown that SGLT2i's promote a general shift to fasting state metabolism characterized by reduced body weight and blood glucose, increase in glucagon/insulin ratio and modest increase in blood ketone levels. Therefore, we investigated the connection between metabolic changes and cardiovascular function in the ob/ob −/− mice; a rodent model of early diabetes with specific focus on coronary microvascular function. Due to leptin deficiency these mice develop metabolic syndrome/diabetes and hepatic steatosis. They also develop cardiac contractile and microvascular dysfunction and are thus a promising model for translational studies of cardiometabolic diseases. We investigated whether this mouse model responded in a human-like manner to empagliflozin treatment in terms of metabolic parameters and tested the hypothesis that it could exert direct effects on coronary microvascular function and contractile performance. Methods: Lean, ob/ob −/− untreated and ob/ob −/− treated with SGLT2i were followed for 10 weeks. Coronary flow velocity reserve (CFVR) and fractional area change (FAC) were monitored with non-invasive Doppler ultrasound imaging. Food intake, urinary glucose excursion and glucose control via HbA1c measurements were followed throughout the study. Liver steatosis was assessed by histology and metabolic parameters determined at the end of the study. Results: Sodium-glucose cotransporter 2 inhibitors treatment of ob/ob −/− animals resulted in a switch to a more catabolic state as observed in clinical studies: blood cholesterol and HbA1c were decreased whereas glucagon/insulin ratio and ketone levels were increased. SGLT2i treatment reduced liver triglyceride, steatosis and alanine aminotransferase, an indicator for liver dysfunction. l-Arginine/ADMA ratio, a marker for endothelial function was increased. SGLT2i treatment improved both cardiac contractile function and coronary microvascular function as indicated by improvement of FAC and CFVR, respectively. Conclusions: Sodium-glucose cotransporter 2 inhibitors treatment of ob/ob −/− mice mimics major clinical findings regarding metabolism and cardiovascular improvements and is thus a useful translational model. We demonstrate that SGLT2 inhibition improves coronary microvascular function and contractile performance, two measures with strong predictive values in humans for CV outcome, alongside with the known metabolic changes in a preclinical model for prediabetes and heart failure.

Physiological functions of the gastrointestinal tract (GIT) are temporally controlled such that they exhibit circadian rhythms. The circadian rhythms are synchronized with the environmental light-dark cycle via signaling from the central circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus, and by food intake. The aim of the study was to determine the extent to which disturbance in the SCN signaling via prolonged exposure to constant light affects circadian rhythms in the liver, duodenum, and colon, as well as to determine whether and to what extent food intake can restore rhythmicity in individual parts of the GIT. Adult male rats were maintained in constant light (LL) for 30 days and fed ad libitum throughout the entire interval or exposed to a restricted feeding (RF) regime for the last 14 days in LL. Locomotor and feeding behaviors were recorded throughout the experiment. On the 30th day, daily expression profiles of clock genes (Per1, Per2, Rev-erbα, and Bmal1) and of clock-controlled genes (Wee1 and Dbp) were measured by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) in the duodenum, colon, and liver. By the end of the LL exposure, rats fed ad libitum had completely lost their circadian rhythms in activity and food intake. Daily expression profiles of clock genes and clock-controlled genes in the GIT were impaired to an extent depending on the tissue and gene studied, but not completely abolished. In the liver and colon, exposure to LL abolished circadian rhythms in expression of Per1, Per2, Bmal1, and Wee1, whereas it impaired, but preserved, rhythms in expression of Rev-erbα and Dbp. In the duodenum, all but Wee1 expression rhythms were preserved. Restricted feeding restored the rhythms to a degree that varied with the tissue and gene studied. Whereas in the liver and duodenum the profiles of all clock genes and clock-controlled genes became rhythmic, in the colon only Per1, Bmal1, and Rev-erbα-but not Per2, Wee1, and Dbp-were expressed rhythmically. The data demonstrate a greater persistence of the rhythmicity of the circadian clocks in the duodenum compared with that in the liver and colon under conditions when signaling from the SCN is disrupted. Moreover, disrupted rhythmicity may be restored more effectively by a feeding regime in the duodenum and liver compared to the colon.

Disruption of circadian machinery appears to be associated with the acceleration of tumor development. To evaluate the function of the circadian clock during neoplastic transformation, the daily profiles of the core clock genes Per1, Per2, RevErba and Bmal1, the clock-controlled gene Dbp and the clock-controlled cell cycle genes Wee1, c-Myc and p21 were detected by real-time RT-PCR in chemically induced primary colorectal tumors, the surrounding normal tissue and in the liver. The circadian rhythmicity of Per1, Per2, Rev-Erba and Dbp was significantly reduced in tumor compared with healthy colon and the rhythmicity of Bmal1 was completely abolished. Interestingly, the circadian expression of Per1, Per2, Rev-Erba and Dbp persisted in the colonic tissue surrounding the tumor but the rhythmic expression of Bmal1 was also abolished. Daily profiles of Wee1, c-Myc and p21 did not exhibit any rhythmicity either in tumors or in the colon of healthy animals. The absence of diurnal rhythmicity of cell cycle genes was partially associated with ageing, because young healthy mice showed rhythmicity in the core clock genes as well as in the Wee1 and p21. In the liver of tumor-bearing mice the clock gene rhythms were temporally shifted. The data suggest that the circadian regulation is distorted in colonic neoplastic tissue and that the genespecific disruption may be also observed in the non-neoplastic tissues. These findings reinforce the role of peripheral circadian clockwork disruption for carcinogenesis and tumor progression.