Circadian clock-mediated regulation of blood pressure

Sleep Neurobiology and the Critical Care Environment

TOPIC

Sleep in the intensive care unit can be poorly consolidated and highly fragmented. This review examines the neurobiology of normal and abnormal sleep, with a focus on the changes that occur in the intensive care unit environment.

CLINICAL RELEVANCE

Patients in the intensive care unit demonstrate a lack of rapid-eye-movement sleep and an inability to effectively transition from light to deep stages of sleep. These abnormalities can adversely affect hemodynamic parameters and physiological and psychological outcomes.

PURPOSE

To describe the brain mechanisms and electroencephalographic characteristics of wakefulness and the different stages of sleep. This review also describes how sleep can be altered by hospitalization in the intensive care unit and how nurses can design interventions that improve sleep and outcomes.

CONTENT COVERED

The review examines sleep mechanisms, including brain electrical activity, regulatory centers in the brain, and circadian and diurnal patterns of sleep and hemodynamic function. Nursing interventions for specific patient risk factors in the intensive care unit are proposed.

Influence of circadian rhythms on sports performance

Chronobiology is the scientific discipline of study of biological rhythms, a term that has gained ground in the sports world. Recently numerous studies have indicated that the time of day in which sports are practiced influences the achievement of good physical performance. The aim of this review was to study the relationship between circadian rhythms and physical performance, according to the latest published data. In addition, the physiological processes involved in the physical response and the differences according to the type of sport and athletes' characteristics were studied. A bibliographic search was carried out through five databases (Pubmed, Scopus, Researcher Gate, Google Scholar, UOC Library), focusing on articles published in the last ten years and written in English and Spanish. 36 papers met the inclusion criteria. Body temperature is a factor that shows a circadian pattern with a marked peak in the later afternoon, time of the day at which physical performance is at its highest, i.e. speed, agility, distance covered, jumping power. The perception of effort is also higher in the afternoon. Regarding the chronotype, evening types seem to be the most affected to do sports out of their optimal time-of-day. The tendency shows more morning types as age increases. Training sessions should be planned according to the optimal time of day for each athlete. It's essential to take into account individual chronotype. The desynchronization of circadian rhythms can cause a decrease in physical performance.

Circadian variations in blood pressure and their implications for the administration of antihypertensive drugs: is dosing in the evening better than in the morning?

: Blood pressure (BP) follows a circadian rhythm with a physiological decrease during the night. Studies have demonstrated that nocturnal BP as well as its dipping pattern during night-time have a significant prognostic importance for mortality and the occurrence of cardiovascular events. Therefore, hypertension management guidelines recommend to ascertain that patients treated for hypertension have well controlled BP values around the clock. To improve hypertension control during the night and eventually further reduce cardiovascular events, it has been proposed by some to prescribe at least one antihypertensive medication at bedtime. In this review, we have examined the data which could support the benefits of prescribing BP-lowering drugs at bedtime. Our conclusion is that there is no convincing evidence that the administration of BP-lowering drugs in the evening provides any significant advantage in terms of quality of BP control, prevention of target organ damage or reduction of cardiovascular events. Before changing practice for unproven benefits, it would be wise to wait for the results of the ongoing trials that are addressing this issue.

Autonomic Nervous System in Obesity and Insulin-Resistance-The Complex Interplay between Leptin and Central Nervous System

The role of the autonomic nervous system in obesity and insulin-resistant conditions has been largely explored. However, the exact mechanisms involved in this relation have not been completely elucidated yet, since most of these mechanisms display a bi-directional effect. Insulin-resistance, for instance, can be caused by sympathetic activation, but, in turn, the associated hyperinsulinemia can activate the sympathetic branch of the autonomic nervous system. The picture is made even more complex by the implicated neural, hormonal and nutritional mechanisms. Among them, leptin plays a pivotal role, being involved not only in appetite regulation and glucose homeostasis but also in energy expenditure. The purpose of this review is to offer a comprehensive view of the complex interplay between leptin and the central nervous system, providing further insights on the impact of autonomic nervous system balance on adipose tissue and insulin-resistance. Furthermore, the link between the circadian clock and leptin and its effect on metabolism and energy balance will be evaluated.

Sex Differences in Circadian Clock Genes and Myocardial Infarction Susceptibility

The growing body of evidence shows a significant difference in the circadian rhythm of cardiovascular disease based on biological sex. The incidence of cardiovascular disease varies between women and men. Additionally, biological sex is vital for the timely application of therapy-chronotherapy, which benefits both sexes. This study aimed to examine the potential difference of single nucleotide polymorphisms (SNPs) of the circadian rhythm genes ARNTL, CLOCK, CRY2 and PER2 in women and men with myocardial infarction. A cross-sectional study was conducted, including 200 patients with myocardial infarction. Altogether, ten single nucleotide polymorphisms in the ARNTL, CLOCK, CRY2 and PER2 genes were analyzed. The Chi-square test yielded statistically significant differences in CLOCK gene rs11932595 polymorphism in a recessive genotype model between women and men with a p-value of 0.03 and an odds ratio 2.66, and a corresponding 95% confidence interval of 1.07 to 6.66. Other analyzed polymorphisms of the circadian rhythm genes ARNTL, CRY2, and PER2 did not significantly differ between the sexes. According to the study's current results, the CLOCK gene's genetic variability might affect myocardial infarction concerning biological sex.

Endothelin B receptors impair baroreflex function and increase blood pressure variability during high salt diet

Baroreflex function is an integral component maintaining consistent blood pressure. Hypertension is often associated with baroreflex dysfunction, and environmental risk factors such as high salt diet exacerbate hypertension in subjects with baroreflex dysfunction. However, the interactions between high salt diet, baroreflex dysfunction, and hypertension are incompletely understood. The endothelin system is another potent mediator of blood pressure control especially in response to a high salt diet. We hypothesized that the endothelin B (ETB) receptor activation on adrenergic nerves decreases baroreflex sensitivity. We utilized male ETB receptor deficient (ETB-def) rats that express functional ETB receptors only on adrenergic nerves and transgenic (TG) controls to evaluate baroreflex function during normal (0.49% NaCl) and high (4.0% NaCl) salt diets. In conscious rats equipped with telemetry, ETB-def rats had an increased lability of systolic blood pressure (SBP) compared to TG controls as indicated by higher standard deviation (SD) of SBP under both normal (10.2 ± 0.6 vs. 12.4 ± 0.9 mmHg, respectively, p = 0.0001) and high (11.7 ± 0.6 vs. 16.1 ± 1.0 mmHg, p = 0.0001) salt diets. In anesthetized preparations, ETB-def rats displayed reduced heart rate (p genotype = 0.0167) and renal sympathetic nerve (p genotype = 0.0022) baroreflex sensitivity. We then gave male Sprague-Dawley rats the selective ETB receptor antagonist, A-192621 (10 mg/kg/day), to block ETB receptors. Following ETB receptor antagonism, even though SBP increased (131 ± 7 before vs. 152 ± 8 mmHg after, p < 0.0001), the lability (standard deviation) of SBP decreased (9.3 ± 2.0 vs. 7.1 ± 1.1 mmHg, p = 0.0155). These data support our hypothesis that ETB receptors on adrenergic nerves contribute to baroreflex dysfunction.

The Complexity of Blood Pressure Fluctuation Mediated the Effects of Hypertension on Walking Speed in Older Adults

Background: Older adults with hypertension often had diminished walking performance. The underlying mechanism through which hypertension affects walking performance, however, has not been fully understood. We here measured the complexity of the continuous systolic (SBP) and diastolic (DBP) blood pressure fluctuation, grade of white matter lesions (WMLs), and cognitive function and used structural equation modeling (SEM) to examine the interrelationships between hypertension, BP complexity, WMLs, cognitive function, and walking speed in single- and dual-task conditions.

Methods: A total of 152 older adults with age > 60 years (90 hypertensive and 62 normotensive participants) completed one MRI scan of brain structure, a finger BP assessment of at least 10 min, Mini-Mental State Examination (MMSE) to assess cognitive function, and 10-meter walking tests in single (i.e., normal walking) and dual tasks (i.e., walking while performing a serial subtraction of three from a random three-digit number). The grade of WMLs was assessed using the total score of Fazekas scale; the complexity of SBP and DBP was measured using multiscale entropy (MSE), and the walking performance was assessed by walking speed in single- and dual-task conditions.

Results: As compared to normotensives, hypertensive older adults had significantly slower walking speed, lower complexity of SBP and DBP, greater grade of WMLs, and poorer cognitive function (p < 0.03). Those with lower BP complexity (β > 0.31, p < 0.003), greater WML grade (β < −0.39, p < 0.0002), and/or poorer cognitive function (β < −0.39, p < 0.0001) had slower walking speed in single- and/or dual-task conditions. The SEM model demonstrated significant total effects of hypertension on walking speed, and such effects were mediated by BP complexity only, or BP complexity, WML grade, and cognitive function together.

Conclusion: This study demonstrates the cross-sectional association between the complexity of continuous beat-to-beat BP fluctuation, WML grade, cognitive function, and walking speed in hypertensive and normotensive older adults, revealing a potential mechanism that hypertension may affect walking performance in older adults through diminished BP complexity, increased WML grade, and decreased cognitive function, and BP complexity is an important factor for such effects. Future longitudinal studies are warranted to confirm the findings in this study.

Blood pressure dipping during REM and non-REM sleep in patients with moderate to severe obstructive sleep apnea

A limited number of papers have addressed the association between non-dipping-blood pressure (BP) obstructive sleep apnea (OSA), and no study has assessed BP-dipping during rapid eye movement (REM) and non-REM sleep in OSA patients. This study sought to noninvasively assess BP-dipping during REM and non-REM (NREM)-sleep using a beat-by-beat measurement method (pulse-transit-time (PTT)). Thirty consecutive OSA patients (men = 50%) who had not been treated for OSA before and who had > 20-min of REM-sleep were included. During sleep, BP was indirectly determined via PTT. Patients were divided into dippers and non-dippers based on the average systolic-BP during REM and NREM-sleep. The studied group had a a median age of 50 (42–58.5) years and a body mass index of 33.8 (27.6–37.5) kg/m². The median AHI of the study group was 32.6 (20.1–58.1) events/h (range: 7–124), and 89% of them had moderate-to-severe OSA. The prevalence of non-dippers during REM-sleep was 93.3%, and during NREM-sleep was 80%. During NREM sleep, non-dippers had a higher waist circumference and waist-hip-ratio, higher severity of OSA, longer-time spent with oxygen saturation < 90%, and a higher mean duration of apnea during REM and NREM-sleep. Severe OSA (AHI ≥ 30) was defined as an independent predictor of non-dipping BP during NREM sleep (OR = 19.5, CI: [1.299–292.75], p-value = 0.03). This short report demonstrated that BP-dipping occurs during REM and NREM-sleep in patients with moderate-to-severe OSA. There was a trend of more severe OSA among the non-dippers during NREM-sleep, and severe OSA was independently correlated with BP non-dipping during NREM sleep.

Assessment of Selected Clock Proteins (CLOCK and CRY1) and Their Relationship with Biochemical, Anthropometric, and Lifestyle Parameters in Hypertensive Patients

BACKGROUND

Circadian rhythms misalignment is associated with hypertension. The aim of the study was to evaluate the concentration of selected clock proteins-cryptochrome 1 (CRY1) and circadian locomotor output cycles kaput (CLOCK) to determine their relationships with biochemical and anthropometric parameters and lifestyle elements (diet, physical activity, and quality of sleep) in hypertensive patients.

METHODS

In 31 females with hypertension (HT) and 55 non-hypertensive women (NHT) the CRY1 and CLOCK concentrations, total antioxidant status (TAS), lipid profile, and glycemia were analyzed. Blood pressure and anthropometric measurements, nutritional, exercise, and sleep analyses were performed.

RESULTS

In the HT group, the CRY1 level was 37.38% lower than in the NHT group. No differences were noted in CLOCK concentration between groups. BMI, FBG, and TG were higher in the HT group compared to the NHT group, while TC, LDL, and HDL levels were similar. The study showed no relationship between CRY1 or CLOCK concentrations and glucose or lipids profile, amount of physical activity, or sleep quality, although CRY1 was associated with some anthropometric indicators. In the HT group, increased CLOCK and CRY1 values were associated with a high TAS level.

CONCLUSIONS

The serum level of CRY1 could be considered in a detailed diagnostic of hypertension risk in populations with abnormal anthropometric indices.

Monitoring daytime differences in moderate intensity exercise capacity using treadmill test and muscle dissection

There is growing interest in medicine and sports in uncovering exercise modifiers that enhance or limit exercise capacity. Here, we detail a protocol for testing the daytime effect on running capacity in mice using a moderate intensity treadmill effort test. Instructions for dissecting soleus, gastrocnemius plantaris, and quadriceps muscles for further analysis are provided as well. This experimental setup is optimized for addressing questions regarding the involvement of daytime and circadian clocks in regulating exercise capacity.

For complete details on the use and execution of this protocol, please refer to Ezagouri et al. (2019).

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Exercise capacity is influenced by the time of day

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Protocol for determining moderate intensity exercise capacity using treadmill test

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Instructions for muscle dissection

Circadian variations of vasoconstriction and blood pressure in physiology and diabetes

The intrinsic vascular smooth muscle contraction and vasoconstriction show time-of-day variations, contributing to the blood pressure circadian rhythm, which is essential for cardiovascular health. This brief review provides an overview of our current understanding of the mechanisms underlying the time-of-day variations of vascular smooth muscle contraction. We discuss the potential contribution of the time-of-day variations of vasoconstriction to the physiological blood pressure circadian rhythm. Finally, we survey the data obtained in the type 2 diabetic db/db mouse model that demonstrate the alterations of the time-of-day variations of vasoconstriction and the nondipping blood pressure in diabetes.

Diurnal variations in the expression of core-clock genes correlate with resting muscle properties and predict fluctuations in exercise performance across the day

Objectives

In this study, we investigated daily fluctuations in molecular (gene expression) and physiological (biomechanical muscle properties) features in human peripheral cells and their correlation with exercise performance.

Methods

21 healthy participants (13 men and 8 women) took part in three test series: for the molecular analysis, 15 participants provided hair, blood or saliva time-course sampling for the rhythmicity analysis of core-clock gene expression via RT-PCR. For the exercise tests, 16 participants conducted strength and endurance exercises at different times of the day (9h, 12h, 15h and 18h). Myotonometry was carried out using a digital palpation device (MyotonPRO), five muscles were measured in 11 participants. A computational analysis was performed to relate core-clock gene expression, resting muscle tone and exercise performance.

Results

Core-clock genes show daily fluctuations in expression in all biological samples tested for all participants. Exercise performance peaks in the late afternoon (15–18 hours for both men and women) and shows variations in performance, depending on the type of exercise (eg, strength vs endurance). Muscle tone varies across the day and higher muscle tone correlates with better performance. Molecular daily profiles correlate with daily variation in exercise performance.

Conclusion

Training programmes can profit from these findings to increase efficiency and fine-tune timing of training sessions based on the individual molecular data. Our results can benefit both professional athletes, where a fraction of seconds may allow for a gold medal, and rehabilitation in clinical settings to increase therapy efficacy and reduce recovery times.

Hydrogen Sulfide Restored the Diurnal Variation in Cardiac Function of Aging Mice

The present study was performed to investigate whether H2S could restore the diurnal variation in cardiac function of aging mice and explore the potential mechanisms. We found that ejection fraction (EF) and fractional shortening (FS) in 3-month-old mice exhibited diurnal variations over a 24-hour period. However, the diurnal variations were disrupted in 18-month-old mice, and there was a decline in EF and FS. In addition, the plasma malondialdehyde (MDA) levels were increased, and H2S concentrations and superoxide dismutase (SOD) activities were decreased in 18-month-old mice. Then, CSE KO mice were used to determine if there was a relationship between endogenous H2S and diurnal variations in EF and FS. There was no difference in 12-hour averaged EF and FS between dark and light periods in CSE KO mice accompanying increased MDA levels and decreased SOD activities in plasma, indicating that deficiency of endogenous H2S blunted diurnal variations of cardiac function. To determine whether oxidative stress disrupted the diurnal variations in cardiac function, D-galactose-induced subacute aging mice were employed. After 3-month D-gal treatment, both 12-hour averaged EF and FS in dark or light periods were decreased; meanwhile, there was no difference in 12-hour averaged EF and FS between dark and light periods. After 3-month NaHS treatment in the D-gal group, the plasma MDA levels were decreased and SOD activities were increased. The EF and FS were lower during the 12-hour light period than those during the 12-hour dark period which was fit to sine curves in the D-gal+NaHS group. Identical findings were also observed in 18-month-old mice. In conclusion, our studies revealed that the disrupted diurnal variation in cardiac function was associated with increased oxidative stress and decreased H2S levels in aging mice. H2S could restore the diurnal variation in cardiac function of aging mice by reducing oxidative stress.

Effect of Sleep Disturbances on Blood Pressure

This review summarizes recent literature addressing the association of short sleep duration, shift work, and obstructive sleep apnea with hypertension risk, blood pressure (BP) levels, and 24-hour ambulatory BP. Observational studies demonstrate that subjectively assessed short sleep increases hypertension risk, though conflicting results are observed in studies of objectively assessed short sleep. Intervention studies demonstrate that mild and severe sleep restriction are associated with higher BP. Rotating and night shift work are associated with hypertension as shift work may exacerbate the detrimental impact of short sleep on BP. Further, studies demonstrate that shift work may increase nighttime BP and reduce BP control in patients with hypertension. Finally, moderate to severe obstructive sleep apnea is associated with hypertension, particularly resistant hypertension. Obstructive sleep apnea is also associated with abnormal 24-hour ambulatory BP profiles, including higher daytime and nighttime BP, nondipping BP, and a higher morning surge. Continuous positive airway pressure treatment may lower BP and improve BP dipping. In conclusion, efforts should be made to educate patients and health care providers about the importance of identifying and treating sleep disturbances for hypertension prevention and management. Empirically supported sleep health interventions represent a critical next step to advance this research area and establish causality.

Sleep phenotype of individuals with autism spectrum disorder bearing mutations in the PER2 circadian rhythm gene

The Per family of genes functions as a primary circadian rhythm maintenance in the brain. Mutations in PER2 are associated with familial advanced sleep-phase syndrome 1 (FASPS1), and recently suggested in delayed sleep phase syndrome and idiopathic hypersomnia. The detection of PER2 variants in individuals with autism spectrum disorder (ASD) and without reported sleep disorders, has suggested a role of circadian-relevant genes in the pathophysiology of ASD. It remains unclear whether these individuals may have, in addition to ASD, an undiagnosed circadian rhythm sleep disorder. The MSSNG database was used to screen whole genome sequencing data of 5,102 individuals with ASD for putative mutations in PER2. Families identified were invited to complete sleep phenotyping consisting of a structured interview and two standardized sleep questionnaires: the Pittsburgh Sleep Quality Index and the Morningness-Eveningness Questionnaire. From 5,102 individuals with ASD, two nonsense, one frameshift, and one de novo missense PER2 variants were identified (0.08%). Of these four, none had a diagnosed sleep disorder. Three reported either a history of, or ongoing sleep disturbances, and one had symptoms highly suggestive of FASPS1 (as did a mutation carrier father without ASD). The individual with the missense variant did not report sleep concerns. The ASD and cognitive profiles of these individuals varied in severity and symptoms. The results support a possible role of PER2-related circadian rhythm disturbances in the dysregulation of sleep overall and sometimes FASPS1. The relationship between dysregulated sleep and the pathophysiology of ASD require further exploration.

Cortisol on Circadian Rhythm and Its Effect on Cardiovascular System

The synthesis and secretion of cortisol are controlled by the hypothalamic–pituitary–adrenal axis. Cortisol exhibits a proper 24-h circadian rhythm that affects the brain, the autonomic nervous system, the heart, and the vasculature that prepares the cardiovascular system for optimal function during these anticipated behavioral cycles. A literature search was conducted using databases such as Google Scholar, PubMed, and Scopus. Relevant search terms included “circadian rhythm and cardiovascular”, “cortisol”, “cortisol and acute coronary syndrome”, “cortisol and arrhythmias”, “cortisol and sudden cardiac death”, “cortisol and stroke”, and “cardioprotective agents”. A total of 120 articles were obtained on the basis of the above search. Lower levels of cortisol were seen at the beginning of sleep, while there was a rise towards the end of sleep, with the highest level reached at the moment the individual wakes up. In the present review, we discuss the role of 11β-hydroxysteroid dehydrogenase (11β-HSD1), which is a novel molecular target of interest for treating metabolic syndrome and type-2 diabetes mellitus. 11β-HSD1 is the major determinant of cortisol excess, and its inhibition alleviates metabolic abnormalities. The present review highlights the role of cortisol, which controls the circadian rhythm, and describes its effect on the cardiovascular system. The review provides a platform for future potential cardioprotective therapeutic agents.

Circadian changes in Alzheimer's disease: Neurobiology, clinical problems, and therapeutic opportunities

The understanding of Alzheimer's disease (AD) pathophysiology is an active area of research, and the traditional focus on hippocampus, amyloid and tau protein, and memory impairment has been expanded with components like neuroinflammation, insulin resistance, and circadian rhythm alterations. The bidirectional vicious cycle of neuroinflammation and neurodegeneration on a molecular level may cause functional deficits already long before the appearance of overt clinical symptoms. Located at the crossroads of metabolic, circadian, and hormonal signaling, the hypothalamus has been identified as another brain region affected by AD pathophysiology. Current findings on hypothalamic dysfunction open a broader horizon for studying AD pathogenesis and offer new opportunities for diagnosis and therapy. While treatments with cholinomimetics and memantine form a first line of pharmacological treatment, additional innovative research is pursued toward the development of antiinflammatory, growth factor, or antidiabetic types of medication. Following recent epidemiological data showing associations of AD incidence with modern societal and "life-style"-related risk factors, also nonpharmacological interventions, including sleep optimization, are being developed and some have been shown to be beneficial. Circadian aspects in AD are relevant from a pathophysiological standpoint, but they can also have an important role in pharmacologic and nonpharmacologic interventions, and appropriate timing of sleep, meals, and medication may boost therapeutic efficacy.

Alcohol suppresses cardiovascular diurnal variations in male normotensive rats: Role of reduced PER2 expression and CYP2E1 hyperactivity in the heart

BACKGROUND AND AIMS

The molecular mechanism of the adverse effects of ethanol on diurnal cardiovascular regulation remains unknown. In separate studies, the cardiac circadian rhythm protein period-2 (PER2) confers cardioprotection and, in other organs, PER2 interaction with the ethanol-metabolizing enzyme CYP2E1 underlies, via heme oxygenase-1 (HO-1) upregulation, tissue injury/dysfunction. Here, we hypothesized that suppressed PER2 expression and elevated CYP2E1/HO-1 levels in the heart underlie the disrupted diurnal cardiovascular rhythm/function in alcohol-fed normotensive rats.

METHODS

In ethanol-fed (5%, w/v; 8 weeks) or isocaloric liquid diet-fed male rats, diurnal changes in blood pressure (BP), heart rate (HR), HR vagal variability index, root mean square of successive beat-to-beat differences in beat-interval duration (rMSSD), and cardiac function were measured by radiotelemetry and echocardiography followed by ex vivo molecular studies.

RESULTS

Radiotelemetry findings showed ethanol-evoked reductions in BP (during the dark cycle), rMSSD (during both cycles), and in diurnal differences in BP and rMSSD. Echocardiography findings revealed significant (p < 0.05) reductions in ejection fraction and fractional shortening (weeks 4-6) in the absence of cardiac remodeling (collagen content). Hearts of ethanol-fed rats exhibited higher (p < 0.05) CYP2E1 activity (50%) and HO-1 expression (63%), along with reduction (p < 0.05) in PER2 levels (29%), compared with the hearts of isocaloric diet-fed control rats.

CONCLUSIONS

Our novel findings implicate upregulations of CYP2E1/HO-1 and downregulation of the circadian rhythm cardioprotective protein PER2, in the heart, in the chronic deleterious diurnal cardiovascular effects of alcohol in male rats.

Circadian mutant mice with obesity and metabolic syndrome are resilient to cardiovascular disease

Obesity and metabolic syndrome commonly underlie cardiovascular disease. Clock^Δ19/Δ19 mice fed a normal diet develop obesity and metabolic syndrome; however, it is not known whether they develop or are resilient to cardiovascular disease. We found that Clock^Δ19/Δ19 mice do not develop cardiac dysfunction, despite their underlying conditions. Moreover, in contrast to wild-type controls fed a high-fat diet (HFD), Clock^Δ19/Δ19 HFD mice still do not develop cardiovascular disease. Indeed, Clock^Δ19/Δ19 HFD mice have preserved heart weight despite their obesity, no cardiomyocyte hypertrophy, and preserved heart structure and function, even after 24 wk of a HFD. To determine why Clock^Δ19/Δ19 mice are resilient to cardiac dysfunction despite their underlying obesity and metabolic conditions, we examined global cardiac gene expression profiles by microarray and bioinformatics analyses, revealing that oxidative stress pathways were involved. We examined the pathways in further detail and found that 1) SIRT-dependent oxidative stress pathways were not directly involved in resilience; 2) 4-hydroxynonenal (4-HNE) increased in wild-type HFD but not Clock^Δ19/Δ19 mice, suggesting less reactive oxygen species in Clock^Δ19/Δ19 mice; 3) cardiac catalase (CAT) and glutathione peroxidase (GPx) increased, suggesting strong antioxidant defenses in the hearts of Clock^Δ19/Δ19 mice; and 4) Pparγ was upregulated in the hearts of Clock^Δ19/Δ19 mice; this circadian-regulated gene drives transcription of CAT and GPx, providing a molecular basis for resilience in the Clock^Δ19/Δ19 mice. These findings shed new light on the circadian regulation of oxidative stress and demonstrate an important role for the circadian mechanism in resilience to cardiovascular disease.NEW & NOTEWORTHY We examined whether obesity and metabolic syndrome underlie the development of cardiac dysfunction in circadian mutant Clock^Δ19/Δ19 mice. Surprisingly, we demonstrate that although Clock^Δ19/Δ19 mice develop metabolic dysfunction, they are protected from cardiac hypertrophy, left ventricular remodeling, and diastolic dysfunction, in contrast to wild-type controls, even when challenged with a chronic high-fat diet. These findings shed new light on the circadian regulation of oxidative stress pathways, which can mediate resilience to cardiovascular disease.

Whole transcriptome analysis of adrenal glands from prenatal glucocorticoid programmed hypertensive rodents

Prenatal glucocorticoid exposure is associated with the development of hypertension in adults. We have previously demonstrated that antenatal dexamethosone (DEX) administration in Wistar-Kyoto dams results in offspring with increased blood pressure coupled with elevated plasma epinephrine levels. In order to elucidate the molecular mechanisms responsible for prenatal DEX-mediated programming of hypertension, a whole-transcriptome analysis was performed on DEX programmed WKY male adrenal glands using the Rat Gene 2.0 microarray. Differential gene expression (DEG) analysis of DEX-exposed offspring compared with saline-treated controls revealed 142 significant DEGs (109 upregulated and 33 downregulated genes). DEG pathway enrichment analysis demonstrated that genes involved in circadian rhythm signaling were most robustly dysregulated. RT-qPCR analysis confirmed the increased expression of circadian genes Bmal1 and Npas2, while Per2, Per3, Cry2 and Bhlhe41 were significantly downregulated. In contrast, gene expression profiling of Spontaneously Hypertensive (SHR) rats, a genetic model of hypertension, demonstrated decreased expression of Bmal1 and Npas2, while Per1, Per2, Per3, Cry1, Cry2, Bhlhe41 and Csnk1D were all upregulated compared to naïve WKY controls. Taken together, this study establishes that glucocorticoid programmed adrenals have impaired circadian signaling and that changes in adrenal circadian rhythm may be an underlying molecular mechanism responsible for the development of hypertension.

Lifestyle interventions for the prevention and treatment of hypertension

Hypertension affects approximately one third of the world's adult population and is a major cause of premature death despite considerable advances in pharmacological treatments. Growing evidence supports the use of lifestyle interventions for the prevention and adjuvant treatment of hypertension. In this Review, we provide a summary of the epidemiological research supporting the preventive and antihypertensive effects of major lifestyle interventions (regular physical exercise, body weight management and healthy dietary patterns), as well as other less traditional recommendations such as stress management and the promotion of adequate sleep patterns coupled with circadian entrainment. We also discuss the physiological mechanisms underlying the beneficial effects of these lifestyle interventions on hypertension, which include not only the prevention of traditional risk factors (such as obesity and insulin resistance) and improvements in vascular health through an improved redox and inflammatory status, but also reduced sympathetic overactivation and non-traditional mechanisms such as increased secretion of myokines.

Association between circadian disruption and diseases: A narrative review

Circadian rhythms play an important role in a wide range of human physiology and pathology. Individuals increasingly experience situations such as night-shift work schedules, likely leading to circadian disruption. Recent studies have also demonstrated that patients with other diseases often show symptoms of circadian disruption as manifested by the sleep-wake cycle and other biological rhythms. Circadian disruption often results in changes to the phase, period, and amplitude of the sleep-wake cycle, melatonin rhythm, and core body temperature. Several cardiometabolic, psychiatric, and neurodegenerative diseases are closely related to circadian disruption. Several interventions are also available, including phototherapy, exogenous melatonin, and exercise. The cumulative findings suggest that circadian disruption can increase risk for some cardiometabolic diseases. Circadian disruption also acts as a concomitant symptom of several psychiatric and neurodegenerative diseases. More attention should be paid to evaluating the impact of circadian disruption on these related diseases, as well as the benefits of the mitigation interventions for both circadian disruption and related diseases.

Circadian disruption, melatonin rhythm perturbations and their contributions to chaotic physiology

The aim of this report is to summarize the data documenting the vital nature of well-regulated cellular and organismal circadian rhythms, which are also reflected in a stable melatonin cycle, in supporting optimal health. Cellular fluctuations in physiology exist in most cells of multicellular organisms with their stability relying on the prevailing light:dark cycle, since it regulates, via specialized intrinsically-photoreceptive retinal ganglion cells (ipRGC) and the retinohypothalamic tract, the master circadian oscillator, i.e., the suprachiasmatic nuclei (SCN). The output message of the SCN, as determined by the light:dark cycle, is transferred to peripheral oscillators, so-called slave cellular oscillators, directly via the autonomic nervous system with its limited distribution. and indirectly via the pineal-derived circulating melatonin rhythm, which contacts every cell. Via its regulatory effects on the neuroendocrine system, particularly the hypothalamo-pituitary-adrenal axis, the SCN also has a major influence on the adrenal glucocorticoid rhythm which impacts neurological diseases and psychological behaviors. Moreover, the SCN regulates the circadian production and secretion of melatonin. When the central circadian oscillator is disturbed, such as by light at night, it passes misinformation to all organs in the body. When this occurs the physiology of cells becomes altered and normal cellular functions are compromised. This physiological upheaval is a precursor to pathologies. The deterioration of the SCN/pineal network is often a normal consequence of aging and its related diseases, but in today's societies where manufactured light is becoming progressively more common worldwide, the associated pathologies may also be occurring at an earlier age.

Extreme dipping: is the cardiovascular risk increased? An unsolved issue

: Extreme dipping (i.e. a marked blood pressure fall during night-time period) is an alteration of circadian blood pressure (BP) rhythm frequently observed in the setting of systemic hypertension as well as in the general population. Some reports have suggested that cardiovascular prognosis in extreme dippers (ED) is similar as in dippers, whereas other studies have documented either a better or worse prognosis in ED. Available information on clinical and prognostic implications of ED is scanty and data provided by studies are controversial. Furthermore, a comprehensive report summarizing the key features of this BP pattern is lacking. The present review focuses on a number of issues concerning ED pattern such as the prevalence and clinical correlates, mechanisms underlying this BP phenotype association with hypertension mediated organ damage (HMOD) and prognostic value in predicting cardiovascular events and all-cause mortality. The reported prevalence of this BP rhythm alteration ranges from 5% to 30%, depending on diagnostic criteria, clinical and demographic characteristics of subjects. Most studies targeting the association of this condition with HMOD failed to find consistent findings in support of an adverse impact of ED on vascular, renal of cardiac structure and function. Available data on ED as compared to low risk reference group (i.e. dippers) do not allow to conclude that high BP variability resulting from a marked BP fall at night adversely affects cardiovascular prognosis at the community level and in the general hypertensive population. Thus, further studies aimed to assess the prognostic significance of ED as well as the impact of therapeutic interventions aimed to normalize this circadian BP pattern, are highly needed.

Chronobiological patterns of acute aortic dissection in central China

BACKGROUND

Acute aortic dissection (AAD) is a life-threatening emergency with poor clinical outcomes. Understanding the chronological patterns of AAD onset would be helpful for identifying the triggers of AAD and preventing this catastrophic event.

METHODS

We collected data from 2048 patients diagnosed with AAD at Tongji Hospital (Wuhan, China) from 2011 to 2018. The χ2 test was used to determine whether a specific period had significantly different seasonal/weekly distributions from other periods. Fourier models were used to analyse the rhythmicity in monthly/circadian distribution.

RESULTS

The mean age was 53.4±10.9 years, and 1161 patients (56.7%) were under 55 years. One thousand six hundred fifty-seven patients (80.9%) were male, and 935 cases (45.7%) were type A dissections. The proportions of patients with comorbid hypertension/diabetes were 60.3% (1234 cases) and 1.8% (36 cases), respectively. A peak was identified in colder periods (winter/December) and a trough in warmer periods (summer/June). No significant variation was observed in weekly distribution. Fourier analysis showed a statistically significant circadian variation (p<0.001) with a nocturnal trough in 2:00-3:00, a morning peak in 9:00-10:00, and an afternoon peak in 16:00-17:00. Subgroup analyses identified circadian rhythmicity in all subgroups except for the female group and younger group (younger than 55 years).

CONCLUSION

Our results confirmed that the onset of AAD exhibits significant seasonal, monthly and circadian patterns. Patients with AAD with different Stanford-type dissections, sexes, ages and hypertension statuses could present different circadian variations. These findings may provide novel perspectives for identifying the triggers of AAD and better preventing this catastrophic event.

Molecular Mechanisms Underlying the Circadian Rhythm of Blood Pressure in Normotensive Subjects

PURPOSE OF REVIEW

Blood pressure (BP) follows a circadian rhythm (CR) in normotensive subjects. BP increases in the morning and decreases at night. This review aims at providing an up-to-date overview regarding the molecular mechanisms underlying the circadian regulation of BP.

RECENT FINDINGS

The suprachiasmatic nucleus (SCN) is the regulatory center for CRs. In SCN astrocytes, the phosphorylated glycogen synthase kinase-3β (pGSK-3β) also follows a CR and its expression reaches a maximum in the morning and decreases at night. pGSK-3β induces the β-catenin migration to the nucleus. During the daytime, the nuclear β-catenin increases the expression of the glutamate excitatory amino acid transporter 2 (EAAT2) and glutamine synthetase (GS). In SCN, EAAT2 removes glutamate from the synaptic cleft of glutamatergic neurons and transfers it to the astrocyte cytoplasm where GS converts glutamate into glutamine. Thus, glutamate decreases in the synaptic cleft. This decreases the stimulation of the glutamate receptors AMPA-R and NMDA-R located on glutamatergic post-synaptic neurons. Consequently, activation of NTS is decreased and BP increases. The opposite occurs at night. Despite several studies resulting from animal studies, the circadian regulation of BP appears largely controlled in normotensive subjects by the canonical WNT/β-catenin pathway involving the SCN, astrocytes, and glutamatergic neurons.

Role of neuronal nitric oxide synthase on cardiovascular functions in physiological and pathophysiological states

This review describes and summarizes the role of neuronal nitric oxide synthase (nNOS) on the central nervous system, particularly on brain regions such as the ventrolateral medulla (VLM) and the periaqueductal gray matter (PAG), and on blood vessels and the heart that are involved in the regulation and control of the cardiovascular system (CVS). Furthermore, we shall also review the functional aspects of nNOS during several physiological, pathophysiological, and clinical conditions such as exercise, pain, cerebral vascular accidents or stroke and hypertension. For example, during stroke, a cascade of molecular, neurochemical, and cellular changes occur that affect the nervous system as elicited by generation of free radicals and nitric oxide (NO) from vulnerable neurons, peroxide formation, superoxides, apoptosis, and the differential activation of three isoforms of nitric oxide synthases (NOSs), and can exert profound effects on the CVS. Neuronal NOS is one of the three isoforms of NOSs, the others being endothelial (eNOS) and inducible (iNOS) enzymes. Neuronal NOS is a critical homeostatic component of the CVS and plays an important role in regulation of different systems and disease process including nociception. The functional and physiological roles of NO and nNOS are described at the beginning of this review. We also elaborate the structure, gene, domain, and regulation of the nNOS protein. Both inhibitory and excitatory role of nNOS on the sympathetic autonomic nervous system (SANS) and parasympathetic autonomic nervous system (PANS) as mediated via different neurotransmitters/signal transduction processes will be explored, particularly its effects on the CVS. Because the VLM plays a crucial function in cardiovascular homeostatic mechanisms, the neuroanatomy and cardiovascular regulation of the VLM will be discussed in conjunction with the actions of nNOS. Thereafter, we shall discuss the up-to-date developments that are related to the interaction between nNOS and cardiovascular diseases such as hypertension and stroke. Finally, we shall focus on the role of nNOS, particularly within the PAG in cardiovascular regulation and neurotransmission during different types of pain stimulus. Overall, this review focuses on our current understanding of the nNOS protein, and provides further insights on how nNOS modulates, regulates, and controls cardiovascular function during both physiological activity such as exercise, and pathophysiological conditions such as stroke and hypertension.

The Night Effect of Anger: Relationship with Nocturnal Blood Pressure Dipping

INTRODUCTION

The circadian pattern of blood pressure is characterized by a physiological drop occurring after sleep onset. The alteration of this phenomenon (non-dipping, extreme dipping, or reverse dipping) is associated with an increased cardiovascular risk. Besides altered autonomic and endocrine circadian rhythms, psychological aspects seem to play a role in this modification. However, the few studies that have analyzed the influence of psychological dimensions on the dipping phenomenon have reported inconsistent results. This study aimed to examine the relationship between anger expression and blood pressure (BP) dipping.

METHODS

We obtained 24 h ambulatory BP measurements from 151 participants and used them to define three groups according to their dipping status: Dippers (N = 65), Non-Dippers (N = 42), and Extreme Dippers (N = 44). Sociodemographic and anamnestic information was collected, and the State-Trait Anger Expression Inventory was used to assess anger.

RESULTS

Analysis of variance evidenced significant higher scores for Trait Anger Temperament and Anger Expression in Extreme Dippers than in both Dippers and Non-Dippers. However, after controlling for confounding variables, there was no significant relationship with trait anger, and only the result concerning the suppression of anger was confirmed.

CONCLUSIONS

These findings suggest that the analysis of some psychological factors, such as anger, could be necessary to better understand differences in nocturnal BP alterations. Trait anger and suppression of anger may contribute to the description and classification of patients who exhibit a maladaptive dipping phenomenon. However, modifiable (i.e., cigarette consumption) and unmodifiable (i.e., age) risk factors appear to mediate this relationship. Although further studies are necessary to explore this association, these results highlight that some aspects of anger can represent risk factors or markers of maladaptive modulation of the dipping phenomenon.

Loss of circadian gene Bmal1 in the collecting duct lowers blood pressure in male, but not female, mice

Kidney function follows a 24-h rhythm subject to regulation by circadian genes including the transcription factor Bmal1. A high-salt diet induces a phase shift in Bmal1 expression in the renal inner medulla that is dependent on endothelin type B (ETB) receptors. Furthermore, ETB receptor-mediated natriuresis is sex dependent. Therefore, experiments tested the hypothesis that collecting duct Bmal1 regulates blood pressure in a sex-dependent manner. We generated a mouse model that lacks Bmal1 expression in the collecting duct, where ETB receptor abundance is highest. Male, but not female, collecting duct Bmal1 knockout (CDBmal1KO) mice had significantly lower 24-h mean arterial pressure (MAP) than flox controls (105 ± 2 vs. 112 ± 3 mmHg for male mice and 106 ± 1 vs. 108 ± 1 mmHg for female mice, by telemetry). After 6 days on a high-salt (4% NaCl) diet, MAP remained significantly lower in male CDBmal1KO mice than in male flox control mice (107 ± 2 vs. 113 ± 1 mmHg), with no significant differences between genotypes in female mice (108 ± 2 vs. 109 ± 1 mmHg). ETB receptor blockade for another 6 days increased MAP similarly in both male and female CDBmal1KO and flox control mice. However, MAP remained lower in male CDBmal1KO mice than in male flox control mice (124 ± 2 vs. 130 ± 2 mmHg). No significant differences were observed between female CDBmal1KO and flox mice during ETB blockade (130 ± 2 vs. 127 ± 2 mmHg). There were no significant genotype differences in amplitude or phase of MAP in either sex. These data suggest that collecting duct Bmal1 has no role in circadian MAP but plays an important role in overall blood pressure in male, but not female, mice.

Time-of-Day-Dependent Physiological Responses to Meal and Exercise

The mammalian circadian clock drives the temporal coordination in cellular homeostasis and it leads the day-night fluctuation of physiological functions, such as sleep/wake cycle, hormonal secretion, and body temperature. The mammalian circadian clock system in the body is classified hierarchically into two classes, the central clock in the suprachiasmatic nucleus (SCN) of the hypothalamus and the peripheral clocks in peripheral tissues such as the intestine and liver, as well as other brain areas outside the SCN. The circadian rhythm of various tissue-specific functions is mainly controlled by each peripheral clock and partially by the central clock as well. The digestive, absorptive, and metabolic capacities of nutrients also show the day-night variations in several peripheral tissues such as small intestine and liver. It is therefore indicated that the bioavailability or metabolic capacity of nutrients depends on the time of day. In fact, the postprandial response of blood triacylglycerol to a specific diet and glucose tolerance exhibit clear time-of-day effects. Meal frequency and distribution within a day are highly related to metabolic functions, and optimal time-restricted feeding has the potential to prevent several metabolic dysfunctions. In this review, we summarize the time-of-day-dependent postprandial response of macronutrients to each meal and the involvement of circadian clock system in the time-of-day effect. Furthermore, the chronic beneficial and adverse effects of meal time and eating pattern on metabolism and its related diseases are discussed. Finally, we discuss the timing-dependent effects of exercise on the day-night variation of exercise performance and therapeutic potential of time-controlled-exercise for promoting general health.

The relation of work-related factors with ambulatory blood pressure and nocturnal blood pressure dipping among aging workers

Objectives

Individuals with reduced nocturnal blood pressure (BP) dipping are at increased risk of cardiovascular disease compared to persons with normal BP dipping. Although the relation of work-related factors and BP has been studied extensively, very little is known of the association between work-related factors and 24-h BP patterns in aging workers. We examined the cross-sectional relation of work-related risk factors, including occupational status, work-time mode, job demands and job control, with ambulatory BP in aging workers, focusing on nocturnal BP dipping.

Methods

208 workers (mean age 62 ± 3 years; 75% women) from two Finnish population-based cohort studies underwent 24-h ambulatory BP monitoring. Work-related factors were inquired using a questionnaire. Nocturnal BP dipping was calculated as [1 − (asleep BP/awake BP)] × 100.

Results

Shift workers demonstrated a higher nocturnal diastolic BP dipping than regular day workers (19% vs. 17%, p = 0.03) and had a significantly higher systolic awake BP than regular day workers (136.5 mmHg vs. 132.5 mmHg, p = 0.03). Participants with high job demands demonstrated a smaller nocturnal systolic BP dipping than participants with low job demands (14% vs. 16%, p = 0.04). We did not observe significant differences in nocturnal systolic or diastolic BP dipping between groups categorized by occupational status or job control.

Conclusions

Although shift workers have a higher daytime BP than regular daytime workers, they exhibit greater nighttime BP dipping. Participants with high job demand had smaller nighttime BP dipping than participants with low job demand. Job control or occupation did not affect the 24-h ambulatory BP profile of aging workers.

Clocking the circadian genes in human embryonic stem cells

Multicellular organisms respond to changing environment which is primarily driven by light from the sun. Essential cyclical processes such as digestion, sleep, migration and breeding are controlled by set of genes know as circadian genes. The core circadian genes comprise of CLOCK, BMAL-1, PERIOD and CYRPTOCHROME that are expressed cyclically and they regulate expression of several genes downstream. The expression of circadian genes has been well studied in multicellular animals; however, it has been shown that stem cells also possess active circadian cycle genes. The circadian cycle genes have been studied in mouse embryonic stem cells and in adult human stem cells. However, there are only few reports of circadian cycle genes in human pluripotent stem cells. We used human embryonic stem cells to investigate the expression of CLOCK, BMAL-1, PERIOD and CYRPTOCHORME genes by RT-PCR at 6, 18 and 22 hours in undifferentiated and differentiated cells. We differentiated human embryonic stem cells spontaneously by adding 10% fetal bovine serum (FBS), and the cells primarily differentiated into ectoderm and mesoderm. We report that CLOCK and BMAL-1 are differentially expressed while PERIOD and CRYPTOCHROME show cyclicity in differentiated and undifferentiated cells. Our results show circadian genes are active in human embryonic stem cells and this needs to be further investigated as human pluripotent stem cells have potential to be used for cell therapy, where they need to synchronize with the body's circadian cycle.

Circadian Variation in Vasoconstriction and Vasodilation Mediators and Baroreflex Sensitivity in Hypertensive Rats

The purpose of this study was to evaluate the relationship between the circadian profile of the vasorelaxing substances calcitonin gene-related peptide (CGRP) and epoxyeicosatrienoic acids (EETs) and the vasconstrictive agent endothelin-1 (ET1) and the daily rhythms of cardiac hemodynamic indices (CHI) and baroreflex (BRS) in Wistar rats with 1 kidney-1 clip model of arterial hypertension (1K-1C AH). The animals were divided into 3 groups: I- sham-operated (SO), II- 4-week and III- 8-week 1K-1C AH rats. Plasma concentration of ET1, CGRP and EET’s were investigated every 4 h. In conscious freely moving 1K-1C AH rats unlike SO animals blood pressure (BP), heart period (HP) and BRS underwent significant circadian fluctuations, with more marked increase in mean values of BP in 8-week hypertensive rats in comparison to 4-week hypertensive rats (179 ± 5 vs. 162 ± 4 mm Hg, p < 0.05). These alterations correlated with more significant reduction in HP (138 ± 5 vs. 150 ± 6 ms, p < 0,05) and BRS (0.44 ± 0.04 vs. 0.58 ± 0.04 ms mm Hg^–1, p < 0.05) in 8-week 1K-1C AH rats. The acrophases of BP in 8-week 1K-1C AH rats in comparison with 4-week were shifted to more late night hours (1:58 a.m. vs. 11:32 p.m.) and in both groups of animals corresponded to lowest circadian plasma levels of CGRP and EETs and to greatest level of ET1. SO rats were characterized by lower values of BP (121 ± 3 mm Hg, p < 0,05) and higher indices of HP (158 ± 2 ms, p < 0,05) and BRS (0.86 ± 0.02 ms mmHg^–1, p < 0,001) in comparison with 1K-1C AH rats 4-week duration. The acrophases of BP, HP and BRS in hypertensive animals were revealed at 14.8 ± 0.5 h, 13.6 ± 0.4 h and 13.1 ± 0.2 h, which correlated with maximal circadian contents of ET1 and CGRP at 24:00 h and EETs at 12:00 h and were shifted in comparison to sham-operated group. In rats with 1K-1C AH, plasma levels of ET1, CGRP and EETs undergo circadian fluctuation with corresponding alterations in CHI and BRS which are more markedly expressed on the late stage of diseases and could be used in future for predictive, preventive, and personalized treatment of arterial hypertension.

Quantity, Quality, and Timing of Carbohydrate Intake and Blood Pressure

PURPOSE OF REVIEW

This review discusses recent evidence on the association of dietary carbohydrates (quantity, quality, and timing of intake) with hypertension (HTN) risk and out-of-clinic blood pressure (BP) measures.

RECENT FINDINGS

Studies on carbohydrate quantity are inconclusive, but low carbohydrate diets may be associated with lower BP. Plant-based carbohydrate-containing foods such as fruits, vegetables, and whole grains may lower HTN risk and 24-h BP. Excessive sugar intakes from sugar-sweetened beverages are associated with higher BP levels and HTN risk, with evidence of a dose-response relationship. Preliminary data suggest that timing of carbohydrate intake may influence HTN risk and 24-h BP. The role of carbohydrate nutrition in HTN's etiology warrants further investigation. Additional studies are needed to investigate the influence of dietary carbohydrates on HTN risk and the circadian pattern of BP, evaluate potential sex and racial/ethnic differences in these associations, and elucidate underlying mechanisms.

Changes in cerebral autoregulation and blood biomarkers after remote ischemic preconditioning

Objective

To determine the effect of remote ischemic preconditioning (RIPC) on dynamic cerebral autoregulation (dCA) and various blood biomarkers in healthy adults.

Methods

A self-controlled interventional study was conducted. Serial measurements of dCA were performed at 7 time points (7, 9, and 11 am; 2, 5, and 8 pm, and 8 am on the next day) without or with RIPC, carried out at 7:20 to 8 am. Venous blood samples were collected at baseline (7 am) and 1 hour after RIPC, and blood biomarkers, including 5 neuroprotective factors and 25 inflammation-related biomarkers, were measured with a quantitative protein chip.

Results

Fifty participants were enrolled (age 34.54 ± 12.01 years, 22 men). Compared with the results on the day without RIPC, dCA was significantly increased at 6 hours after RIPC, and the increase was sustained for at least 24 hours. After RIPC, 2 neuroprotective factors (glial cell-derived neurotrophic factor and vascular endothelial growth factor-A) and 4 inflammation-related biomarkers (transforming growth factor-β1, leukemia inhibitory factor, matrix metallopeptidase-9, and tissue inhibitor of metalloproteinase-1) were significantly elevated compared with their baseline levels. Conversely, monocyte chemoattractant protein-1 was significantly lower compared with its baseline level.

Conclusions

RIPC induces a sustained increase of dCA from 6 to at least 24 hours after treatment in healthy adults. In addition, several neuroprotective and inflammation-related blood biomarkers were differentially regulated shortly after RIPC. The increased dCA and altered blood biomarkers may collectively contribute to the beneficial effects of RIPC on cerebrovascular function.

ClinicalTrials.gov identifier:

NCT02965547.

Blood Pressure Circadian Variation, Cognition and Brain Imaging in 90+ Year-Olds

Purpose: To analyze the relationship between blood pressure (BP) variables, including circadian pattern, and cognition in 90+ year-olds.

Methods: Twenty-four hour ambulatory BP monitoring was completed on 121 participants drawn from a longitudinal study of aging and dementia in the oldest-old. Various measures of BP and its variability, including nocturnal dipping, were calculated. Each person was given both a neuropsychological test battery covering different cognitive domains and a neurological examination to determine cognitive status. Seventy-one participants had a brain magnetic resonance imaging (MRI) scan.

Results: Participants ranged in age from 90 to 102 years (mean = 93), about two-thirds were female, and nearly 80% had at least some college education. Mean nocturnal dips differed significantly between cognitively normal (n = 97) and impaired individuals (n = 24), with cognitively normal participants having on average greater nocturnal dips [6.6% vs. 1.3%, p = 0.006 for systolic BP (SBP); 11% vs. 4.4%, p = 0.002 for diastolic BP (DBP)]. Nocturnal dips were also related to performance on select cognitive test scores (especially those related to language, recent memory and visual-spatial ability), with individuals who performed below previously established median norms having significantly smaller nocturnal dips (both SBP and DBP) than those above the median. DBP reverse dippers had larger mean white matter hyperintensities (WMH as percent of total brain volume; 1.7% vs. 1.2%, 1.1% and 1.0% in extreme dippers, dippers, non-dippers) and a greater proportion had lobar cerebral microbleeds (CMBs; 44% vs. 0%, 7%, 16%, p < 0.05). Impaired participants had higher mean WMH than those with normal cognition (1.6% vs. 1.0% p = 0.03) and more tended to have CMB (31% vs. 20%, p = n.s.).

Conclusion: These findings suggest that cognitive dysfunction is associated with dysregulation in the normal circadian BP pattern. Further study is warranted of the potential role of WHM and CMB as mediators of this association.

The Clock Mechanism Influences Neurobiology and Adaptations to Heart Failure in Clock∆19/∆19 Mice With Implications for Circadian Medicine

In this study we investigated the role of the circadian mechanism on cognition-relevant brain regions and neurobiological impairments associated with heart failure (HF), using murine models. We found that the circadian mechanism is an important regulator of healthy cognitive system neurobiology. Normal Clock∆19/∆19 mice had neurons with smaller apical dendrite trees in the medial prefrontal cortex (mPFC), and hippocampus, showed impaired visual-spatial memory, and exhibited lower cerebrovascular myogenic tone, versus wild types (WT). We then used the left anterior descending coronary artery ligation model to investigate adaptations in response to HF. Intriguingly, adaptations to neuron morphology, memory, and cerebrovascular tone occurred in differing magnitude and direction between Clock∆19/∆19 and WT mice, ultimately converging in HF. To investigate this dichotomous response, we performed microarrays and found genes crucial for growth and stress pathways that were altered in Clock∆19/∆19 mPFC and hippocampus. Thus these data demonstrate for the first time that (i) the circadian mechanism plays a role in neuron morphology and function; (ii) there are changes in neuron morphology and function in HF; (iii) CLOCK influences neurobiological gene adaptations to HF at a cellular level. These findings have clinical relevance as patients with HF often present with concurrent neurocognitive impairments. There is no cure for HF, and new understanding is needed to reduce morbidity and improve the quality of life for HF patients.

Autonomic nerves and circadian control of renal function

Cardiovascular and renal physiology follow strong circadian rhythms. For instance, renal excretion of solutes and water is higher during the active period compared to the inactive period, and blood pressure peaks early in the beginning of the active period of both diurnal and nocturnal animals. The control of these rhythms is largely dependent on the expression of clock genes both in the central nervous system and within peripheral organs themselves. Although it is understood that the central and peripheral clocks interact and communicate, few studies have explored the specific mechanism by which various organ systems within the body are coordinated to control physiological processes. The renal sympathetic nervous innervation has long been known to have profound effects on renal function, and because the sympathetic nervous system follows strong circadian rhythms, it is likely that autonomic control of the kidney plays an integral role in modulating renal circadian function. This review highlights studies that provide insight into this interaction, discusses areas lacking clarity, and suggests the potential for future work to explore the role of renal autonomics in areas such as blood pressure control and chronic kidney disease.

Direct and indirect inhibition of the circadian clock protein Per1: effects on ENaC and blood pressure

Circadian rhythms govern physiological functions and are important for overall health. The molecular circadian clock comprises several transcription factors that mediate circadian control of physiological function, in part, by regulating gene expression in a tissue-specific manner. These connections are well established, but the underlying mechanisms are incompletely understood. The overall goal of this study was to examine the connection among the circadian clock protein Period 1 (Per1), epithelial Na⁺ channel (ENaC), and blood pressure (BP) using a multipronged approach. Using global Per1 knockout mice on a 129/sv background in combination with a high-salt diet plus mineralocorticoid treatment, we demonstrated that loss of Per1 in this setting is associated with protection from hypertension. Next, we used the ENaC inhibitor benzamil to demonstrate a role for ENaC in BP regulation and urinary Na⁺ excretion in 129/sv mice. We targeted Per1 indirectly using pharmacological inhibition of Per1 nuclear entry in vivo to demonstrate altered expression of known Per1 target genes as well as a BP-lowering effect in 129/sv mice. Finally, we directly inhibited Per1 via genetic knockdown in amphibian distal nephron cells to demonstrate, for the first time, that reduced Per1 expression is associated with decreased ENaC activity at the single channel level.

Autoimmune Disease-Associated Hypertension

Purpose of Review

To highlight important new findings on the topic of autoimmune disease-associated hypertension.

Recent Findings

Autoimmune diseases including systemic lupus erythematosus and rheumatoid arthritis are associated with an increased risk for hypertension and cardiovascular disease. A complex interaction among genetic, environmental, hormonal, and metabolic factors contribute to autoimmune disease susceptibility while promoting chronic inflammation that can lead to alterations in blood pressure. Recent studies emphasize an important mechanistic role for autoantibodies in autoimmune disease-associated hypertension. Moving forward, understanding how sex hormones, neutrophils, and mitochondrial dysfunction contribute to hypertension in autoimmune disease will be important.

Summary

This review examines the prevalent hypertension in autoimmune disease with a focus on the impact of immune system dysfunction on vascular dysfunction and renal hemodynamics as primary mediators with oxidative stress as a main contributor.

Angiotensin-(1-7) Receptor Mas in Hemodynamic and Thermoregulatory Dysfunction After High-Level Spinal Cord Injury in Mice: A Pilot Study

Spinal cord injury (SCI) above mid-thoracic levels leads to autonomic dysfunction affecting both the cardiovascular system and thermoregulation. The renin-angiotensin system (RAS) which is a potent regulator of blood pressure, including its novel beneficial arm with the receptor Mas could be an interesting target in post-SCI hemodynamics. To test the hypothesis that hemodynamics, activity and diurnal patterns of those are more affected in the Mas deficient mice post-SCI we used a mouse model of SCI with complete transection of spinal cord at thoracic level 4 (T4-Tx) and performed telemetric monitoring of blood pressure (BP) and heart rate (HR). Our data revealed that hypothermia deteriorated physiological BP and HR control. Preserving normothermia by keeping mice at 30°C prevented severe hypotension and bradycardia post-SCI. Moreover, it facilitated rapid return of diurnal regulation of BP, HR and activity in wild type (WT) mice. In contrast, although Mas deficient mice had comparable reacquisition of diurnal HR rhythm, they showed delayed recovery of diurnal rhythmicity in BP and significantly lower nocturnal activity. Exposing mice with T4-Tx (kept in temperature-controlled cages) to 23°C room temperature for one hour at different time-points post-SCI, demonstrated their inability to maintain core body temperature, Mas deficient mice being significantly more impaired than WT littermates. We conclude that Mas deficient mice were more resistant to acute hypotension, delayed nocturnal recovery, lower activity and more severely impaired thermoregulation. The ambient temperature had significant effect on hemodynamics and, thus it should be taken into account when assessing cardiovascular parameters post-SCI in mice.

Dynamic Cerebral Autoregulation Remains Stable During the Daytime (8 a.m. to 8 p.m.) in Healthy Adults

Many functions of the human body possess a daily rhythm, disruptions of which often lead to disease. Dynamic cerebral autoregulation (dCA) stabilizes the cerebral blood flow to prompt normal neural function. However, whether dCA is stable across the day remains unknown. This study aimed to investigate the daily rhythm of dCA. Fifty-one healthy adults (38.294 ± 13.279 years, 40 females) were recruited and received six dCA measurements per individual that were conducted at predefined time points: 8:00, 9:00, 11:00, 14:00, 17:00, and 20:00. Although the blood pressure fluctuated significantly, there was no statistical difference in phase difference and gain (autoregulatory parameters) across the six time points. This study demonstrates that dCA remains stable during the interval from 8 a.m. to 8 p.m. and underscores the importance of stable dCA in maintaining cerebral blood flow and neural function.

Chronobiology in nephrology: the influence of circadian rhythms on renal handling of drugs and renal disease treatment

INTRODUCTION

Chronobiology studies the phenomenon of rhythmicity in living organisms. The circadian rhythms are genetically determined and regulated by external synchronizers (the daylight cycle). Several biological processes involved in the pharmacokinetics and pharmacodynamics of drugs are subjected to circadian variations. Chronopharmacology studies how biological rhythms influence pharmacokinetics, pharmacodynamics, and toxicity, and determines whether time-of-day administration modifies the pharmacological characteristics of the drug. Chronotherapy applies chronopharmacological studies to clinical treatments, determining the best biological time for dosing: when the beneficial effects are maximal and the incidence and/or intensity of related side effects and toxicity are minimal. Most water-soluble drugs or drug metabolites are eliminated by urine through the kidney. The rate of drug clearance in the urine depends on several intrinsic variables related to renal function including renal blood flow, glomerular filtration rate, the ability of the kidney to reabsorb or to secrete drugs, urine flow, and urine pH, which influences the degree of urine acidification. Curiously, all these variables present a circadian behavior in different mammalian models.

CONCLUSION

The circadian rhythms have influence in the renal physiology, pathophysiology, and pharmacology, and these data should be taken into account in clinical nephrology practice.

Circadian Rhythms and Mitochondria: Connecting the Dots

Circadian rhythms provide a selective advantage by anticipating organismal nutrient needs and guaranteeing optimal metabolic capacity during active hours. Impairment of circadian rhythms is associated with increased risk of type 2 diabetes and emerging evidence suggests that metabolic diseases are linked to perturbed clock machinery. The circadian clock regulates many transcriptional–translational processes influencing whole cell metabolism and particularly mitochondrial activity. In this review, we survey the current literature related to cross-talks between mitochondria and the circadian clock and unravel putative molecular links. Understanding the mechanisms that link metabolism and circadian responses to transcriptional modifications will provide valuable insights toward innovative therapeutic strategies to combat the development of metabolic disease.

RECENT ADVANCES IN UNDERSTANDING THE CIRCADIAN CLOCK IN RENAL PHYSIOLOGY

Accumulating evidence suggests a critical role for the molecular circadian clock in the regulation of renal function. Here, we consider the most recent advances in our understanding of the relationship between the circadian clock and renal physiology.