Basal Circadian Rhythm Research Articles

121 - Menadione Induced Reset of Circadian Superoxide Rhythms in Human Colon Cancer Cells

The effectiveness of some anticancer therapeutics have been reported to be dependent on the circadian timing of their administration. But this strategy is not widely used probably because the underlying rhythms and their alterations by external zeitgebers are not fully understood. Rhythms in the pseudo-steady-state (PSS) levels of particular intracellular reactive species (RS), the crucial effectors of cytotoxicity induced by many anticancer drugs in cancer cells have not been reported so far. In this work, we have shown that superoxide radicals have a basal circadian rhythm in the colon cancer cell line HCT116, which was reset by superoxide generating anti-cancer drug menadione. We have found a p53 dependent reset of superoxide rhythm in menadione treated HCT116 wt human colon cancer cells. The reset in period of oscillation was found to have a linear correlation with the drug concentration, given by the equation, T (in hours) = 22.57-0.96[menadione concentration in µM] and was absent in the p53-/- variant of the cell line. The 2 fold higher sensitivity of the wt cells to menadione with an IC50 value of 15 µM as compared to 30 µM for the p53-/- variant suggests a significant role for the reset of superoxide rhythms in sensitizing the cells to menadione induced cytotoxicity. Further, to understand the mode of action of the drug menadione, we propose a reaction scheme using a superoxide – ERK – p53 – MnSOD loop for the rhythm reset and construct a representative mathematical model. The model generated results were found to be consistent with experimental observations. Further, the model predicts the changes in the concentration profiles of various species in the system, which are difficult to observe experimentally in real time.

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis in irritable bowel syndrome.

Enhanced stress responsiveness has been implicated as a potential mechanism contributing to the pathophysiology of irritable bowel syndrome (IBS), and should be reflected in altered function of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system. Both of these systems can modulate mucosal immune function. The aims of this study were: (i) to characterize the basal circadian rhythm of adrenocorticotropin hormone (ACTH) and cortisol in IBS vs healthy controls; (ii) to compare stimulated ACTH, cortisol and noradrenaline responses to a pelvic visceral stressor (sigmoidoscopy) in IBS and controls; and (iii) to correlate neuroendocrine responses with colonic mucosal cytokine expression and symptoms in IBS. Two separate studies were conducted in women. In Study 1, basal cortisol levels were analysed in 41 IBS and 25 controls using 24-h collections of plasma ACTH and cortisol (q10 min sampling). In Study 2, 10 IBS patients with diarrhoea (IBS-D) and 10 controls underwent sigmoidoscopy with measurements of stimulated neuroendocrine responses and cytokine mRNA expression in colonic tissue. Basal ACTH levels were significantly blunted (P < 0.05), while basal and stimulated plasma cortisol levels were higher in patients. Basal cortisol levels prior to an experimental visceral stressor positively correlated with anxiety symptoms (P < 0.004), but not IBS symptoms. Irritable bowel syndrome patients with diarrhoea had significantly decreased mRNA expression of mucosal cytokines [interleukin (IL)-2, IL-6] in the sigmoid colon vs controls (P < 0.05). Although dysregulations in stress-responsive systems such as the HPA axis and mucosal immune function are demonstrated in IBS, they do not appear to have a primary role in modulating IBS severity and abdominal pain.

Circadian cortisol rhythms in healthy boys and girls: relationship with age, growth, body composition, and pubertal development.

To provide basic information on the normal functioning of the hypothalamus-pituitary-adrenal axis in relation to pubertal development, growth (weight and height), body composition, and gender and to obtain reference data for serum cortisol concentrations in children, we investigated the basal circadian rhythm of serum cortisol in a group of 235 healthy children (162 boys and 73 girls). The age range was between 2.2-18.5 yr. Serum cortisol was analyzed from venous blood samples taken at 1400, 1800, 2200, 0200, 0400, 0600, and 1000 h. No evidence was found for differences in temporal placement or level of the circadian cortisol rhythm in relation to age, growth, or body composition. However, we found a broad range of cortisol levels in a healthy population, with individual mean diurnal levels ranging from 100-510 nmol/L. Regardless of high or low mean diurnal cortisol levels, repeated measurements within and between pubertal stages indicated that an individual remains in his or her cortisol range throughout pubertal development. In conclusion, the present study shows that 1) serum cortisol levels do not correlate with either age or gender; 2) there is a large and significant interindividual variability in endogenous mean diurnal cortisol levels; and 3) despite this variability between individuals, there is no correlation between cortisol levels and either body composition or growth rate. This suggests that the variability in cortisol levels is an expression of normal homeostasis rather than pathology.

Regulation of the hypothalamo-pituitary-adrenal axis during stress: feedback, facilitation and feeding

Stressors stimulate the release of corticotropin-releasing factor and/or vasopressin from the hypothalamic paraventricular nuclei causing secretion of adrenocorticotropin from the pituitary and corticosteroids from the adrenal cortex. Corticosteroids inhibit activity in the adrenocortical system by association with high affinity, type I and lower affinity type II corticosteroid receptors in brain. Despite the potent inhibitory effects of exogenously infused corticosteroids on basal and stress-induced adrenocorticotropin, sustained or repeated stress causes facilitated responses to novel stressors. Feedback and facilitation of stress responses are observed during the trough of the basal circadian rhythm but not at the peak. We discuss evidence for the hypothesis that the circadian rhythm in energy acquisition determines the rhythms in stress responsiveness and suggest that the adrenocortical system is embedded in a larger hypothalamic neural network that regulates energy balance.

Impaired type II glucocorticoid-receptor function in mice bearing antisense RNA transgene

Glucocorticoids, in conjunction with their cognate receptors, exert negative-feedback effects on the hypothalamus-pituitary-adrenal axis, suppressing adrenal steroid secretions. Two types of corticosteroid receptor, distinguishable by their ability to bind corticosterone, have been identified as classical mineralocorticoid (type I) and glucocorticoid (type II) receptors by cloning their complementary DNAs. The type I receptor controls the basal circadian rhythm of corticosteroid secretion. Both receptor types are involved in negative feedback, but the type II receptor may be more important for terminating the stress response as it is the only one to be increased in animals rendered more sensitive to corticosteroid negative-feedback effects. Here we create a transgenic mouse with impaired corticosteroid-receptor function by partially knocking out gene expression with type II glucocorticoid receptor antisense RNA. We use this animal to study the glucocorticoid feedback effect on the hypothalamus-pituitary-adrenal axis.

そしゃく筋深部温のＲＡＭパック記録法

This study presented the development of the electrical isolated data collecting system by means of the special movement of random access memory pack [RAM-pack] between the A/D converter and the computer.In the normal male aged 29, the deep temperatures of forehead and masseter muscle, the skin temperature of masseter muscle, and the room temperature were sampled at a rate of 15 sec/time during sleep throughout five consecutive nights.It was shown that 1) This system was able to collect the data of body temperatures in security; 2) Each body temperature showed the short-lasting changes superimposed on the long-lasting change.The nocturnal variation might be characterized of a basal circadian rhythm.

Variations in evaporation and body temperatures during sleep in man

The thermal balance in man was investigated during nocturnal sleep in neutral and warm environments (from 32 to 39.5 degrees C, 45%rh). Changes of body temperatures and skin evaporation were continuously monitored throughout the whole night. In neutral conditions (32 and 34 degrees C) body temperature and skin evaporation decreased during the night, following the circadian rhythm deltaT sk = -0.34 degrees C; deltaT re = -0.52 degrees C;deltaE = -12 W-m-2. In warm conditions, body temperatures and evaporation remained steady. Marked fluctuations of body temperatures and evaporation occurred synchronously with the rapid eye movement (REM) periods. Each REM period induced phasic increase of Tsk reaching +2 degrees C in some cases, with a cessation of evaporation. Tre showed upward and downward rhythmical waves synchronously with REM sleep occurrence. The nocturnal variations of thermal balance were characterized by two rhythms: a basal circadian rhythm and superimposed on it a rhythm conditioned by occurrence of REM sleep every 80-90 min. The phasic changes of body temperatures and evaporation only appeared with REM's. The results suggest that the nervous integrative function conditioning the patterns of sleep, conditions also the phasic cyclic changes of thermoregulatory function.