Dosing‐Time–Dependent Differences in Lipopolysaccharide‐Induced Liver Injury in Rats

Circadian rhythms and environmental disturbances – underexplored interactions

Biological rhythms control the life of virtually all organisms, impacting numerous aspects ranging from subcellular processes to behaviour. Many studies have shown that changes in abiotic environmental conditions can disturb or entrain circadian (∼24 h) rhythms. These expected changes are so large that they could impose risks to the long-term viability of populations. Climate change is a major global stressor affecting the fitness of animals, partially because it challenges the adaptive associations between endogenous clocks and temperature – consequently, one can posit that a large-scale natural experiment on the plasticity of rhythm–temperature interactions is underway. Further risks are posed by chemical pollution and the depletion of oxygen levels in aquatic environments. Here, we focused our attention on fish, which are at heightened risk of being affected by human influence and are adapted to diverse environments showing predictable changes in light conditions, oxygen saturation and temperature. The examined literature to date suggests an abundance of mechanisms that can lead to interactions between responses to hypoxia, pollutants or pathogens and regulation of endogenous rhythms, but also reveals gaps in our understanding of the plasticity of endogenous rhythms in fish and in how these interactions may be disturbed by human influence and affect natural populations. Here, we summarize research on the molecular mechanisms behind environment–clock interactions as they relate to oxygen variability, temperature and responses to pollutants, and propose ways to address these interactions more conclusively in future studies.

Evolving roles of circadian rhythms in liver homeostasis and pathology

Circadian clock in mammals is determined by a core oscillator in the suprachiasmatic nucleus (SCN) of the hypothalamus and synchronized peripheral clocks in other tissues. The coherent timing systems could sustain robust output of circadian rhythms in response to the entrainment controlled environmentally. Disparate approaches have discovered that clock genes and clock-controlled genes (CCGs) exist in nearly all mammalian cell types and are essential for establishing the mechanisms and complexity of internal time-keeping systems. Accumulating evidence demonstrates that the control of homeostasis and pathology in the liver involves intricate loops of transcriptional and post-translational regulation of clock genes expression. This review will focus on the recent advances with great importance concerning clock rhythms linking liver homeostasis and diseases. We particularly highlight what is currently known of the evolving insights into the mechanisms underlying circadian clock . Eventually , findings during recent years in the field might prompt new circadian-related chronotherapeutic strategies for the diagnosis and treatment of liver diseases by coupling these processes.

Time-dependent inhibitory effect of lipopolysaccharide injection on Per1 and Per2 gene expression in the mouse heart and liver

Lipopolysaccharide (LPS) is a pathogen-associated large molecule responsible for sepsis-related endotoxic shock, and the heart is one of the most common organs adversely affected. LPS is reported to increase serum TNFalpha levels and reduce Per1 and Per2 gene expression. Therefore, in this experiment, we determined the time-dependent effects of LPS on heart rate (HR) and circadian gene expression in the mouse heart and liver. HR of the LPS group was significantly elevated 2 and 8 h after injection compared to the control group. A significant percent increase in HR was observed at ZT6, 12, and 18. LPS increased Tnfalpha mRNA expression in the heart and liver at ZT6, 18, and 24. A time-dependent effect of LPS on reduction of Per1 and Per2 gene expression was also observed in the heart and liver. In order to examine the effect of LPS on cell damage, we examined apoptosis-related gene expression after LPS injection. Bax mRNA expression level of the LPS group was higher than that of the control group 8 and 26 h after injection. On the other hand, Bcl2 mRNA expression level of the LPS group was lower than that of the control group 2 and 26 h after injection. Dexamethasone strongly attenuated the LPS-induced increase of serum TNFalpha without significant change in Per1 and Per2 gene expression in the heart. In conclusion, the present results demonstrated that LPS exerts a time-dependent inhibitory effect on Per1 and Per2 gene expression in the heart and liver. The chronopharmacological lethal effect of LPS may be related to the time-dependent increase of serum TNFalpha level and simultaneously high level of Per2 gene expression in the heart and liver between ZT12-18. Taken together, chronopharmacological effect of LPS may be related to not only sickness behavior syndrome and mortality, but also circadian rhythm systems.

Dosing-time dependent effect of dexamethasone on bone density in rats

AIMS

While glucocorticoids are widely used to treat patients with various diseases, they often cause adverse effects such as bone fractures. In this study, we investigated whether the decrease in bone density induced by glucocorticoid therapy was ameliorated by optimizing a dosing-time.

MAIN METHODS

Rats were administered with dexamethasone (Dex) orally (1mg/kg/day) for 6weeks at a resting or an active period. After the end of the treatment, bone density of femur, biomarkers of bone formation and resorption, and other biomedical variables were measured.

KEY FINDINGS

Bone density of femur was significantly decreased by the 6-week treatment with Dex, and the degree of decrease in the 14 HALO (hours after light on) dosing group (an active period) was larger than that in the 2 HALO dosing group (a resting period). Although urinary calcium excretion was accelerated by Dex treatment, secondary hyperparathyroidism was not detected. Histomorphometry analysis showed that Dex suppressed bone resorption, which was larger in the 2 HALO than in the 14 HALO groups. These data indicate that Dex equally suppressed bone formation in the 2 and 14 HALO groups, but inhibited bone resorption more in the 2 HALO than in the 14 HALO groups.

SIGNIFICANCE

This study shows that the decrease in bone density induced by Dex was changed by its dosing-time.