Sex difference in the daily rhythm of hepatic P450 monooxygenase activities in rats is regulated by growth hormone release

Effect of endurance exercise training on liver gene expression in male and female mice

Chronic endurance exercise is a therapeutic strategy in the treatment of many chronic diseases in humans, including the prevention and treatment of metabolic diseases such as diabetes mellitus. Metabolic, cardiorespiratory, and endocrine pathways targeted by chronic endurance exercise have been identified. In the liver, however, the cellular and molecular pathways that are modified by exercise and have preventive or therapeutic relevance to metabolic disease need to be elucidated. The mouse model used in the current study allows for the quantification of a human-relevant exercise "dosage". In this study we show hepatic gene expression differences between sedentary female and sedentary male mice and that chronic exercise modifies the transcription of hepatic genes related to metabolic disease and steatosis in both male and female mice. Chronic exercise induces molecular pathways involved in glucose tolerance, glycolysis, and gluconeogenesis while producing a decrease in pathways related to insulin resistance, steatosis, fibrosis, and inflammation. Given these findings, this mouse exercise model has potential to dissect the cellular and molecular hepatic changes following chronic exercise with application to understanding the role that chronic exercise plays in preventing human diseases. Novelty: Exercise modifies the hepatic gene expression and hepatic pathways related to metabolic disease in male and female mice. Sex differences were seen in hepatic gene expression between sedentary and exercised mice. The mouse exercise model used in this study allows for application and evaluation of exercise effects in human disease.

Assessing circadian rhythms during prolonged midazolam infusion in the pediatric intensive care unit (PICU) children

BACKGROUND

This study evaluates possible circadian rhythms during prolonged midazolam infusion in 27 pediatric intensive care unit (PICU) children under mechanical ventilation.

METHODS

Blood samples for midazolam and 1-OH-midazolam assay were collected throughout the infusion at different times of the day. The blood pressure, heart rate and body temperature were recorded every hour for the rhythms analysis. Population nonlinear mixed-effect modeling with NONMEM was used for data analysis.

RESULTS

A two-compartment model for midazolam pharmacokinetics and a one-compartment model for midazolam metabolite adequately described the data. The 24 h profiles of all monitored physiological parameters were greatly disturbed/abolished in comparison with the well-known 24 h rhythmic patterns in healthy subjects. There was no significant circadian rhythm detected with respect to midazolam pharmacokinetics, its active metabolite pharmacokinetics and all monitored parameters.

CONCLUSIONS

We concluded that the light-dark cycle did not influence midazolam pharmacokinetics in intensive care units children. Also, endogenous rhythms in critically ill and sedated children are severely disturbed and desynchronized. Our results confirmed that it is necessary to adjust the dose of midazolam to the patient's body weight. The low value of midazolam clearances observed in our study was probably caused by mechanical ventilation, which was shown to decrease the cardiac output.

Circadian modulation of hepatic transcriptome in transgenic rats expressing human growth hormone

The secretory profile of growth hormone (GH) is sexually dimorphic in rats. In male transgenic (TG) rats expressing human GH (hGH) that we generated, the circulating levels of both hGH and endogenous GH are flattened with no male-type pulsatility. To elucidate the regulatory role of episodic GH profile on the liver, the hepatic transcriptome of male TG rats at the middle of the light and dark phases was characterized by genome-wide analyses as compared with that of male wild-type (WT) rats. Transcripts commonly up- or down-regulated regardless of the lighting conditions in TG rats were mainly enriched in the metabolism of xenobiotics. In TG rats, the gene expression profile was functionally feminized, verifying that the sexually dimorphic profile of GH rather than genetic sexuality is a stronger sex-determining factor on the hepatic transcriptome. The common transcripts which fluctuated during the day in both TG and WT rats were enriched in circadian rhythm signaling, and physiological rhythmicity was considered to be finely interconnected with liver metabolism via sexually dimorphic GH secretion. In contrast, some genes were differentially regulated in TG rats at only one of two time points measured, and others were fluctuated daily in only one genotype. In particular, some genes involved in the GH signaling pathway were included, suggesting the signal transduction is circadian-modulated depending upon the GH profile. Our transcriptome analyses clarified the regulatory role of episodic GH profile on the liver and strengthen the functional link between sexually dimorphic GH secretion, liver metabolism, and its circadian regulation.

Sex and circadian modulatory effects on rat liver as assessed by transcriptome analyses

The present study was designed to fully uncover sex and circadian modulatory effects on rat liver. Hepatic transcriptome analyses were performed at 4 hr intervals of a day-night cycle using young adult male and female rats. Sexually dimorphic genes, which were identified by a cross-sex comparison of time series data, included representative sex-predominant genes such as male- or female-predominant cytochrome P450 subfamilies (Cyp2c11, Cyp2c12, Cyp2c13, and Cyp3a2), sulfotransferases, and glutathione S-transferase Yc2. The identified sexually dimorphic genes were over-represented in the metabolism of retinols, xenobiotics, linoleic acids, or androgen and estrogen, or bile acid biosynthesis. Furthermore, transcription factor targets modeling suggested that transcription factors SP1, hepatocyte nuclear factor 4-alpha (HNF4-alpha), and signal transducer and activator of transcription 5b (STAT5b) serve as core nodes in the regulatory networks. On the other hand, Fourier transform analyses extracted universal circadian-regulated genes in both sexes. The circadian-regulated genes included clock or clock-controlled genes such as aryl hydrocarbon receptor nuclear translocator-like (Arntl), period homolog 2 (Per2), and D site albumin promoter binding protein (Dbp). The extracted cyclic genes were over-represented in major tissue activities, e.g. the urea cycle and the metabolism of amino acids, fatty acids, or glucose, indicating that the major liver functions are under circadian control. The transcription factor targets modeling suggested that transcription factors SP1, HNF4-alpha, and c-Myc proto-oncogene protein (c-MYC) serve as major hubs in the circadian-regulatory gene networks. Interestingly, transcription factors SP1 and HNF4-alpha are likely to orchestrate not only sexually dimorphic, but also circadian-regulated genes even though each criterion was rather mutually exclusive. This suggests the cross-talk between those regulations. Sexual dimorphism is likely to interact with circadian rhythmicity via overlapping gene regulatory networks on rat liver.

Patient variation in veterinary medicine--part II--influence of physiological variables

In veterinary medicine, the characterization of a drug's pharmacokinetic properties is generally based upon data that are derived from studies that employ small groups of young healthy animals, often of a single breed. In Part I of the series, we focused on the potential influence of disease processes, stress, pregnancy and lactation on drug pharmacokinetics. In this Part II of the series, we consider other covariates, such as gender, heritable traits, age, body composition, and circadian rhythms. The impact of these factors with respect to predicting the relationship between dose and drug exposure characteristics within an animal population is illustrated through the use of Monte Carlo simulations. Ultimately, an appreciation of these potential influences will improve the prediction of situations when dose adjustments may be appropriate.

Assessing circadian rhythms in propofol PK and PD during prolonged infusion in ICU patients

This study evaluates possible circadian rhythms during prolonged propofol infusion in patients in the intensive care unit. Eleven patients were sedated with a constant propofol infusion. The blood samples for the propofol assay were collected every hour during the second day, the third day, and after the termination of the propofol infusion. Values of electroencephalographic bispectral index (BIS), arterial blood pressure, heart rate, blood oxygen saturation and body temperature were recorded every hour at the blood collection time points. A two-compartment model was used to describe propofol pharmacokinetics. Typical values of the central and peripheral volume of distribution and inter-compartmental clearance were V_C = 27.7 l, V_T = 801 l, and CL_D = 2.73 l/min. The systolic blood pressure (SBP) was found to influence the propofol metabolic clearance according to Cl (l/min) = 2.65·(1 − 0.00714·(SBP − 135)). There was no significant circadian rhythm detected with respect to propofol pharmacokinetics. The BIS score was assessed as a direct effect model with EC₅₀ equal 1.98 mg/l. There was no significant circadian rhythm detected within the BIS scores. We concluded that the light–dark cycle did not influence propofol pharmacokinetics and pharmacodynamics in intensive care units patients. The lack of night–day differences was also noted for systolic blood pressure, diastolic blood pressure and blood oxygenation. Circadian rhythms were detected for heart rate and body temperature, however they were severely disturbed from the pattern of healthy patients.

Correlation of axon size and myelin occupancy in rats prenatally exposed to methamphetamine

The abuse of methamphetamine (MA) and other psychostimulants is a social and medical problem. In particular, the use of these drugs by pregnant women results in an increased number of children exposed prenatally to psychostimulants. Our previous work has demonstrated that prenatal exposure to MA affects the normal development of the rat visual system due to alterations of biochemical mechanisms and oxidative stress. It was also demonstrated that prenatal exposure to MA affects the dopaminergic system of the rat retina and optic nerve (ON) myelination. The present work was conducted to evaluate the effects of prenatal exposure to MA on the development of the ON in terms of axon growth and the myelin sheath. Pregnant female rats were given 5 mg/kg/day MA, subcutaneously (s.c.), in 0.9% saline from gestational day (GD) 8 to 22. The pair-fed control group was injected s.c. with an isovolumetric dose of 0.9% saline. Qualitative analysis was performed using representative electron ultramicrographs. Quantitative analysis was performed at an electron microscopic level on ON cross sections; parameters measured included myelinated/unmyelinated ratio, outer axon mean area, inner axon mean area, myelin mean area, myelin occupancy and distribution of axons by size. The ON of prenatally MA-exposed rats presented a higher rate of deformed axons and slighter lamellar separation. At PND 21, the average outer axon area of MA-treated males was significantly reduced. The average inner axon area only showed a significant difference between MA and control males for axons with an area of less than 0.3 microm(2). The average myelin area of MA-treated males was significantly reduced, and in MA-treated females was only significantly reduced in axons with an area of less than 0.3 microm(2). The percentage of myelin occupancy was significantly affected in MA-treated males, and in MA-treated females in the group of axons with an area of more than 0.3 microm(2). At PND 14 no significant differences were found between MA and control groups. The spectrum of ON myelinated axon size of MA-treated animals was shifted to the left at PND 14 and PND 21 for both genders. These results are in agreement with previous animal studies of prenatal and perinatal exposure to drugs of abuse. Taken together, these data indicate that the ON is vulnerable to early exposure to MA which causes developmental changes and may interfere with the functioning of the visual system.

Reciprocal relationships between general (Propofol) anesthesia and circadian time in rats

Several common postdischarge symptoms, such as sleep disorders, headache, drowsiness or general malaise, evoke disturbances of circadian rhythms due to jet lag (ie crossing time zones) or shift work rotation. Considering that general anesthesia is associated with numerous effects on the central nervous system, we hypothesized that it may also act on the circadian timing system. We first determined the effects of the circadian timing on general anesthesia. We observed that identical doses of propofol showed marked circadian fluctuations in duration of effects, with a peak at the middle of the resting period (ie 7 h after lights on). Then, we examined the effects of general anesthesia on circadian timing, by analysing stable free-running circadian rhythms (ie in constant environmental conditions), an experimental approach used widely in circadian biology. Free-running rats were housed in constant darkness and temperature to assess possible phase-shifting effects of propofol anesthesia according to the time of the day. When administered around (+/-2 h) the daily rest/activity transition point, a 30-min propofol anesthesia induced a 1-h phase advance in the free-running rest-activity rhythm, while anesthesia had no significant resetting effect at other times of the day. Anesthesia-induced hypothermia was not correlated with the phase-shifting effects of propofol anesthesia. From our results, anesthesia itself can reset circadian timing, and acts as a synchronizing cue for the circadian clock.

Effects of restricted feeding on daily fluctuations of hepatic functions including p450 monooxygenase activities in rats

Hepatic P450 monooxygenase activities, assessed by measurement of 7-alkoxycoumarin O-dealkylase (ACD) activities, show obvious daily fluctuations in male rats with high values during the dark period and low values during the light period. We have already confirmed that the ACD activities are controlled by the suprachiasmatic nucleus (SCN), which is well known as the oscillator of circadian rhythm. Recently, it is reported that circadian oscillators exist not only in the SCN but also in peripheral organs. To date, it is unclear which circadian oscillators predominantly drive the daily fluctuations of hepatic ACD activities. To address this question, we examined the effects of restricted feeding, which uncouples the circadian oscillators in the liver from the central pacemaker in the SCN, on the daily fluctuations in hepatic ACD activities in male rats. Here we show that restricted feeding inverts the oscillation phase of the daily fluctuations in hepatic ACD activities. Regarding the hepatic P450 content, there were no fluctuations between the light and dark periods under ad libitum and restricted feeding conditions. Therefore, it is considered that the daily fluctuations in hepatic ACD activities are predominantly driven by the circadian factors in peripheral organs rather than by the oscillator in the SCN directly.

Effect of dietary administration of genistein, nonylphenol or ethinyl estradiol on hepatic testosterone metabolism, cytochrome P-450 enzymes, and estrogen receptor alpha expression

The objective of this study was to examine effects of estrogenic agents of varying potencies (genistein, p-nonylphenol, and ethinyl estradiol) on hepatic testosterone metabolism, cytochrome P-450 (CYP450) enzymes, and ERalpha expression. These endpoints were examined as potential biomarkers of, and contributors to, endocrine disruptive activity. Exposure occurred during critical developmental periods, from gestational day 7 through weaning via the mothers' diet. Thereafter, rats were exposed via their diet to the compounds until puberty (postnatal day 50). Testosterone hydroxylase and 5alpha-reductase activities, CYP2C and CYP3A levels were determined. In general, the compounds were more active in male rats than female rats. The only effect observed in female rats was at the 250 ppm genistein dose, in which an approximately 40% increase in 5alpha-reductase activity was observed. In male rats, genistein treatment had mixed effects on testosterone metabolism. The 1250 ppm dose decreased both CYP2C and CYP3A protein levels. Nonylphenol had the most profound effects on testosterone metabolism and CYP450 expression in male rats, with effects occurring at doses as low as 25 ppm. An increase in 5alpha-reductase activity and a decrease in the formation of 16alpha-OH-, 2alpha-OH-testosterone metabolites, CYP2C and CYP3A protein were observed. EE2 decreased the formation of several testosterone metabolites and CYP2C protein. All compounds had some effect on hepatic ERalpha expression, although a consistent effect was not observed. This study demonstrates that the test compounds can influence hepatic testosterone hydroxylase activity and CYP450 expression, as well as ERalpha expression, although these activities cannot be directly related to estrogenic activity.