Reproducibility of the circadian rhythms of serum cortisol and melatonin in healthy subjects: a study of three different 24-h cycles over six weeks

The Potential of Circadian Realignment in Rheumatoid Arthritis

In this short review, we discuss evidence supporting the modulation of peripheral circadian systems as a therapeutic strategy for rheumatoid arthritis (RA). We first review the role of proinflammatory cytokines and oxidative stress, two of the primary mediators of chronic inflammation in RA, and their regulation by circadian clock machinery. We further highlight the role of environmental and metabolic signals in regulating the central and peripheral circadian clocks, with an emphasis on seasonal variations in photoperiod and rhythmic metabolic input, respectively. Finally, we hypothesize that the entrainment and realignment of peripheral clock rhythms have the ability to modulate these mediators, improving clinical outcomes in RA patients. Our discussion emphasizes the use of light therapy and time-restricted feeding for entraining peripheral clocks either via the entrainment of the central circadian clock in suprachiasmatic nuclei (SCN) or directly by uncoupling the peripheral circadian clocks from SCN. In doing so, we highlight the use of nonpharmacologic interventions as a potential strategy for improving clinical outcomes in chronic inflammatory conditions such as RA.

Alpha-synuclein, epigenetics, mitochondria, metabolism, calcium traffic, & circadian dysfunction in Parkinson's disease. An integrated strategy for management

The motor deficits which characterise the sporadic form of Parkinson's disease arise from age-related loss of a subset of dopamine neurons in the substantia nigra. Although motor symptoms respond to dopamine replacement therapies, the underlying disease process remains. This review details some features of the progressive molecular pathology and proposes deployment of a combination of nutrients: R-lipoic acid, acetyl-l-carnitine, ubiquinol, melatonin (or receptor agonists) and vitamin D3, with the collective potential to slow progression of these features. The main nutrient targets include impaired mitochondria and the associated oxidative/nitrosative stress, calcium stress and impaired gene transcription induced by pathogenic forms of alpha- synuclein. Benefits may be achieved via nutrient influence on epigenetic signaling pathways governing transcription factors for mitochondrial biogenesis, antioxidant defences and the autophagy-lysosomal pathway, via regulation of the metabolic energy sensor AMP activated protein kinase (AMPK) and the mammalian target of rapamycin mTOR. Nutrients also benefit expression of the transcription factor for neuronal survival (NR4A2), trophic factors GDNF and BDNF, and age-related calcium signals. In addition a number of non-motor related dysfunctions in circadian control, clock genes and associated metabolic, endocrine and sleep-wake activity are briefly addressed, as are late-stage complications in respect of cognitive decline and osteoporosis. Analysis of the network of nutrient effects reveals how beneficial synergies may counter the accumulation and promote clearance of pathogenic alpha-synuclein.

Human studies on hypothalamo-pituitary-adrenal (HPA) axis

The daily rhythm of the hypothalamo-pituitary-adrenal (HPA) axis is regulated by the central clock in the suprachiasmatic nucleus. Cortisol, a glucocorticoid, acts as a secondary messenger between the central clock and the peripheral tissues. Changes in clock time, as seen in shift workers, alters the HPA axis and results in metabolic disturbances associated with ill health. Depression, anorexia nervosa and obstructive sleep apnoea, are associated with cortisol rhythm phase shifts and increased cortisol exposure. Higher nocturnal cortisol exposure is observed in patients with Cushing's syndrome and adrenal incidentalomas with autonomous cortisol secretion and is associated with insulin resistance, and increased cardiovascular risk and mortality. A decrease in cortisol rhythm amplitude is seen in adrenal insufficiency, and despite replacement, patients have an impaired quality of life and increased mortality. Research on cortisol replacement has focused on replacing the cortisol daily rhythm by subcutaneous hydrocortisone infusions and oral modified release hydrocortisone formulations with the aim of improving disease control and quality of life.

The Hepato-Hypothalamic-Pituitary-Adrenal-Renal Axis: Mathematical Modeling of Cortisol’s Production, Metabolism, and Seasonal Variation

Cortisol dynamics are governed by the integration of influences from the suprachiasmatic nucleus (SCN), the hypothalamic-pituitary-adrenal (HPA) axis, and metabolic enzymes, such as the 11β–hydroxysteroid dehydrogenase (HSD) family, which are highly expressed in hepatic and renal tissue. The coordinated regulation of cortisol dynamics is essential for the maintenance of a healthy state, and aberrant cortisol circadian rhythms are associated with various pathophysiological conditions. The duration of the light-dark cycle, or photoperiod, which regulates SCN activity, varies seasonally, and the shorter photoperiod winter season is associated with elevated cortisol levels, peak inflammatory disease incidence, and symptom exacerbation. Elevated expression and activity of 11β-HSD1 protein, assumed to also occur during the winter, have been allied with numerous inflammatory conditions. A comprehensive understanding of the communication between the underlying regulatory mechanisms of cortisol as well as how changes in their activity could lead to the development of disease is yet to be elucidated. In this work, we propose the use of a semimechanistic mathematical model to explore the impact of the hepato-hypothalamic-pituitary-adrenal-renal axis in modulating neuroendocrine-immune system dynamics. Our model predicts the predominance of a winter proinflammatory state and that genetic variations could alter 11β-HSD enzyme functionality, rendering certain subpopulations more susceptible to disease as a consequence of HPA axis dysregulation.

Circadian rhythms in blood pressure, heart rate, hormones, and on polysomnographic parameters in severe obstructive sleep apnea syndrome patients: effect of continuous positive airway pressure

INTRODUCTION

Seventeen male patients with severe obstructive sleep apnea syndrome (OSAS; apnea-hypopnea index>30/h) were monitored by polysomnography in the sleep lab before and after about 8 weeks of continuous positive airway pressure (CPAP). Twelve of the patients were hypertensive, but treated by antihypertensive drugs. The circadian rhythms in blood pressure (BP) and heart rate were determined by ambulatory BP monitoring and motor activity was monitored by a motion logger. As the sympathetic tone is reported to be increased in sleep apnea, the circadian rhythm in plasma norepinephrine was studied in parallel and as a marker rhythm of the biological clock plasma melatonin was determined around the clock by radioimmunoassay.

RESULTS

Level and rhythm in BP and heart rate were not significantly affected by CPAP in this group of patients, but the number of dippers increased after CPAP intervention. The high 24 h plasma values of norepinephrine were lowered by CPAP therapy. In contrast, melatonin values were disturbed in OSAS patients with a loss in nocturnal increase; this pattern was not corrected by CPAP. Sleep functions (deep sleep, slow wave sleep, rapid eye movement sleep, arousal index, apnea-hypopnea index, desaturation index) were disturbed in OSAS patients as monitored by polysomnography and were significantly improved by CPAP therapy.

CONCLUSION

The study indicates that BP-controlled hypertensive patients with OSAS can additionally benefit from CPAP therapy by increasing the number of dippers. This treatment significantly improved sleep functions and OSAS symptoms. In addition, arousal movements at night were also reduced and the high sympathetic tone during early morning hours was also decreased. However, there is still an indication of a disturbed function of the biological clock as the loss in the rhythm in plasma melatonin was not corrected by CPAP.

Association between light at night, melatonin secretion, sleep deprivation, and the internal clock: Health impacts and mechanisms of circadian disruption

Exposure to Artificial Light At Night (ALAN) results in a disruption of the circadian system, which is deleterious to health. In industrialized countries, 75% of the total workforce is estimated to have been involved in shift work and night work. Epidemiologic studies, mainly of nurses, have revealed an association between sustained night work and a 50-100% higher incidence of breast cancer. The potential and multifactorial mechanisms of the effects include the suppression of melatonin secretion by ALAN, sleep deprivation, and circadian disruption. Shift and/or night work generally decreases the time spent sleeping, and it disrupts the circadian time structure. In the long run, this desynchronization is detrimental to health, as underscored by a large number of epidemiological studies that have uncovered elevated rates of several diseases, including cancer, diabetes, cardiovascular risks, obesity, mood disorders and age-related macular degeneration. It amounts to a public health issue in the light of the very substantial number of individuals involved. The IARC has classified shift work in group 2A of "probable carcinogens to humans" since "they involve a circadian disorganization". Countermeasures to the effects of ALAN, such as melatonin, bright light, or psychotropic drugs, have been proposed as a means to combat circadian clock disruption and improve adaptation to shift and night work. We review the evidence for the ALAN impacts on health. Furthermore, we highlight the importance of an in-depth mechanistic understanding to combat the detrimental properties of exposure to ALAN and develop strategies of prevention.

Melatonin and cortisol secretion profile in patients with pineal cyst before and after pineal cyst resection

A pineal cyst is a benign affection of the human pineal gland on the borderline between pathology and normality. Only a small percentage of patients present with symptoms and a surgical treatment is indicated in highly selected cases. A melatonin secretion in patients with a pineal cyst before and after a pineal cyst resection has not been studied yet and the effect of surgery on human metabolism is unknown. The present study examined melatonin, cortisol and blood glucose secretion profiles perioperatively in a surgical group of 4 patients. The control group was represented by 3 asymptomatic patients with a pineal cyst. For each patient, 24-h circadian secretion curves of melatonin, cortisol and glycemia were acquired. An analysis of melatonin profiles showed an expected diurnal pattern with the night peak in patients before the surgery and in the control group. In contrast, melatonin levels in patients after the surgery were at their minimum throughout the whole 24-h period. The cortisol secretion was substantially increased in patients after the surgery. Blood glucose sampling showed no statistically significant differences. Clinical results demonstrated statistically significant headache relief measured by Visual Analogue Scale in patients after the surgery. Despite the small number of examined patients, we can conclude that patients with a pineal cyst preserved the physiological secretion of the hormone melatonin while patients who underwent the pineal cyst resection experienced a loss of endogenous pineal melatonin production, which equated with pinealectomy. Surprisingly, cortisol secretion substantially increased in patients after the surgery.

The Mood Rhythm Instrument: development and preliminary report

OBJECTIVE

To describe the initial steps in the development and validation of a new self-reported instrument designed to assess daily rhythms of mood symptoms, namely, the Mood Rhythm Instrument.

METHODS

A multidisciplinary group of experts took part in systematic meetings to plan the construction of the instrument. Clarity of items, their relevance to evaluation of mood states, and the consistency of findings in relation to the available evidence on the biological basis of mood disorders were investigated. The internal consistency of the questionnaire was evaluated through Cronbach's alpha.

RESULTS

All of the items proposed in a first version were well rated in terms of clarity. The items more frequently rated as "rhythmic" were related to the somatic symptoms of mood. Their peaks in 24 hours were more frequent in the morning. The items associated with affective symptoms of mood were rated as less rhythmic, and their peak in 24 hours occurred more frequently in the afternoon and evening. Males and females behaved more similarly with respect to somatic than behavioral-affective items. The second version of the Mood Rhythm Instrument had a Cronbach's alpha of 0.73.

CONCLUSION

The proposed Mood Rhythm Instrument may be able to detect individual rhythms of cognitive and behavioral measures associated with mood states. Validation in larger samples and against objective measures of rhythms, such as actigraphy, is warranted.

Is afternoon cortisol more reliable than waking cortisol in association studies of children with an ASD?

Salivary cortisol may be used as a biomarker of stress and anxiety in children with an Autism Spectrum Disorder (ASD) and is particularly valuable in studies of the association between stress-related cortisol concentrations and other factors such as comorbid disorders or aspects of the ASD phenotype. Although protocols for the collection of cortisol shortly after waking are often based on the assumption of the presence of a diurnal rhythm in cortisol, that rhythm may not be as reliable in children with an ASD as in non-ASD children. Alternatively, collecting cortisol during the afternoon may represent a more reliable procedure with less inter-participant variability.

Characterization and novel analyses of acute stress response patterns in a population-based cohort of young adults: influence of gender, smoking, and BMI

Dysregulation of the biological stress response system has been implicated in the development of psychological, metabolic, and cardiovascular disease. Whilst changes in stress response are often quantified as an increase or decrease in cortisol levels, three different patterns of stress response have been reported in the literature for the Trier Social Stress Test (TSST) (reactive-responders (RR), anticipatory-responders (AR) and non-responders (NR)). However, these have never been systematically analyzed in a large population-based cohort. The aims of this study were to examine factors that contribute to TSST variation (gender, oral contraceptive use, menstrual cycle phase, smoking, and BMI) using traditional methods and novel analyses of stress response patterns. We analyzed the acute stress response of 798, 18-year-old participants from a community-based cohort using the TSST. Plasma adrenocorticotrophic hormone, plasma cortisol, and salivary cortisol levels were quantified. RR, AR, and NR patterns comprised 56.6%, 26.2%, and 17.2% of the cohort, respectively. Smokers were more likely to be NR than (RR or AR; adjusted, p < 0.05). Overweight and obese subjects were less likely to be NR than the other patterns (adjusted, p < 0.05). Males were more likely to be RR than NR (adjusted, p = 0.05). In addition, we present a novel AUC measure (AUCR), for use when the TSST baseline concentration is higher than later time points. These results show that in a young adult cohort, stress-response patterns, in addition to other parameters vary with gender, smoking, and BMI. The distribution of these patterns has the potential to vary with adult health and disease and may represent a biomarker for future investigation.

Measurement in saliva from neurotypical adults of biomarkers pertinent to autism spectrum disorders

Aim:

Measure biomarkers pertinent to autism in saliva from humans.

Materials & methods:

At 7:30 PM (reading instructions) and 8:30 PM (hearing instructions), neurotypical adults (6 M, 6 F) each spat into tubes containing protease inhibitors. Cells were counted, samples aliquoted, frozen and thawed. Rationale was given for choice of biomarkers. ELISA: CD26, IL-12, carnitine, C4B, GSH, GSSG, MT-2, testosterone, IFN-γ. Mass spectrometry: cystine, glutamine, glutamic acid, GABA, serotonin. Electrochemiluminescentimmunoassay: cortisol. Radioimmunoassay: melatonin.

Results:

Cells averaged 2.16 × 10⁶/ml. M > F: CD-26, C4B, MT-2. Testosterone, cortisol. Glutamine, glutamic acid, IFN-γ, melatonin and GSSG were measurable. Remaining biomarkers were measured in <50% of samples. Concentrations were equal at both times.

Conclusion:

Saliva can be collected by literate individuals without added instruction. Ten biomarkers were measurable.

The Association between Primary Open-Angle Glaucoma and Blood Pressure: Two Aspects of Hypertension and Hypotension

Glaucoma is the second leading cause of blindness worldwide. Although the mechanism of the development of primary open-angle glaucoma (POAG) is not fully understood, elevated intraocular pressure (IOP) is considered the most important risk factor. Several vascular factors have also been identified as risk factors and can lead to hypoperfusion of the optic nerve head and thus may play an important role in the pathogenesis and progression of POAG. The results of the present study suggest that both high and low blood pressure (BP) are associated with an increased risk of POAG based on a comprehensive literature review. Elevated BP is associated with elevated IOP, leading to increased risk of glaucoma, but excessive BP lowering in glaucoma patients may cause a drop in ocular perfusion pressure (OPP) and subsequent ischemic injury. The relationship between IOP, OPP, and BP suggests that the relationship between BP and glaucoma progression is U-shaped.

Stress Response of Veterinary Students to Gynaecological Examination of Horse Mares - Effects of Simulator-Based and Animal-Based Training

Invasive procedures in animals are challenging for veterinary students who may perceive a gynaecological examination of mares as stressful. Simulator-based training may reduce stress. In this study, students received equine gynaecology training 4 times either on horses (group H; n = 14) or a teaching simulator (group SIM; n = 13). One day and 14 days thereafter, their diagnostic skills were tested on horses (skills tests 1 and 2). During the skills tests, the students' stress response was analysed by heart rate, heart rate variability (HRV) parameters SDRR (standard deviation of beat-to-beat [RR] interval) and RMSSD (root-mean-square of successive RR differences), and salivary cortisol. In addition, students answered a questionnaire on their perceived stress. Sympathetic activation with increased heart rate (p < 0.001) occurred in both skills tests. In test 1, this increase was more pronounced in SIM than in H students (time × group p < 0.01). HRV decreased in students of both groups (p < 0.001). In skills test 1, this decrease was more pronounced for SIM than for H students (between groups and time × group p < 0.01 for SDRR and p < 0.05 for RMSSD). High cortisol concentrations before the skills tests may indicate an anticipatory stress response. Subjective stress perception of students was higher in skills test 1 vs 2 (p < 0.01). In skills test 2, H students felt more stressed than SIM students (p < 0.01). Self-assessment thus differed from physiological stress parameters. In conclusion, gynaecological examination of mares evoked a moderate stress response in veterinary students, which was more evident after simulator-based than animal-based training.

Human peripheral clocks: applications for studying circadian phenotypes in physiology and pathophysiology

Most light-sensitive organisms on earth have acquired an internal system of circadian clocks allowing the anticipation of light or darkness. In humans, the circadian system governs nearly all aspects of physiology and behavior. Circadian phenotypes, including chronotype, vary dramatically among individuals and over individual lifespan. Recent studies have revealed that the characteristics of human skin fibroblast clocks correlate with donor chronotype. Given the complexity of circadian phenotype assessment in humans, the opportunity to study oscillator properties by using cultured primary cells has the potential to uncover molecular details difficult to assess directly in humans. Since altered properties of the circadian oscillator have been associated with many diseases including metabolic disorders and cancer, clock characteristics assessed in additional primary cell types using similar technologies might represent an important tool for exploring the connection between chronotype and disease, and for diagnostic purposes. Here, we review implications of this approach for gathering insights into human circadian rhythms and their function in health and disease.

Circadian timing of metabolism in animal models and humans

Most living beings, including humans, must adapt to rhythmically occurring daily changes in their environment that are generated by the Earth's rotation. In the course of evolution, these organisms have acquired an internal circadian timing system that can anticipate environmental oscillations and thereby govern their rhythmic physiology in a proactive manner. In mammals, the circadian timing system coordinates virtually all physiological processes encompassing vigilance states, metabolism, endocrine functions and cardiovascular activity. Research performed during the past two decades has established that almost every cell in the body possesses its own circadian timekeeper. The resulting clock network is organized in a hierarchical manner. A master pacemaker, located in the suprachiasmatic nucleus (SCN) of the hypothalamus, is synchronized every day to the photoperiod. In turn, the SCN determines the phase of the cellular clocks in peripheral organs through a wide variety of signalling pathways dependent on feeding cycles, body temperature rhythms, oscillating bloodborne signals and, in some organs, inputs of the peripheral nervous system. A major purpose of circadian clocks in peripheral tissues is the temporal orchestration of key metabolic processes, including food processing (metabolism and xenobiotic detoxification). Here, we review some recent findings regarding the molecular and cellular composition of the circadian timing system and discuss its implications for the temporal coordination of metabolism in health and disease. We focus primarily on metabolic disorders such as obesity and type 2 diabetes, although circadian misalignments (shiftwork or 'social jet lag') have also been associated with the aetiology of human malignancies.

Pharmacodynamic Studies to Demonstrate Bioequivalence of Oral Inhalation Products

In the session on "Pharmacodynamic studies to demonstrate efficacy and safety", presentations were made on methods of evaluating airway deposition of inhaled corticosteroids and bronchodilators, and systemic exposure indirectly using pharmacodynamic study designs. For inhaled corticosteroids, limitations of measuring exhaled nitric oxide and airway responsiveness to adenosine for anti-inflammatory effects were identified, whilst measurement of 18-h area under the cortisol concentration-time curve was recommended for determining equivalent systemic exposure. For bronchodilators, methacholine challenge was recommended as the most sensitive method of determining the relative amount of β-agonist or anti-muscarinic agent delivered to the airways. Whilst some agencies, such as the Food and Drug Administration (FDA), do not require measuring systemic effects when pharmacokinetic measurements are feasible, the European Medicines Agency requires measurement of heart rate and serum potassium, and some require serial electrocardiograms when bioequivalence is not established by pharmacokinetic (PK) studies. The Panel Discussion focused on whether PK would be the most sensitive marker of bioequivalence. Furthermore, there was much discussion about the FDA draft guidance for generic fluticasone propionate/salmeterol. The opinion was expressed that the study design is not capable of detecting a non-equivalent product and would require an unfeasibly large sample size.

Pain perception in healthy young men is modified by time-of-day and is modality dependent

OBJECTIVE

Several physiological processes exhibit 24-hour oscillations termed circadian rhythms. Despite numerous investigations on the circadian dynamics of pain perception, findings related to this issue remain inconsistent. This study aimed to assess the effect of time-of-day on multimodal experimental pain perception in healthy males, including "static" and "dynamic" quantitative sensory tests.

DESIGN

A random order tests were performed in the morning, afternoon and evening.

SUBJECTS

Forty-eight healthy males (25.9 ± 4.7 years old).

METHODS

Three different pain modalities i) mechanical (pain threshold, tolerance, and intensity), ii) heat (pain threshold and intensity), iii) cold (pain threshold measured in °C and in seconds and cold pain tolerance and intensity) utilizing nine "static" pain parameters, and two "dynamic" pain paradigms i) temporal summation and ii) conditioned pain modulation were assessed in each session.

RESULTS

Pain scores varied significantly in six pain parameters during the day. Specifically, lower pain scores were found in the morning for cold pain threshold (in seconds and in °C), cold pain intensity, cold pain tolerance, heat pain threshold and intensity. There were no significant diurnal differences in the mechanical evoked pain parameters or in either of the "dynamic" pain paradigms.

CONCLUSIONS

Thermal pain scores varies during the day and morning seems to be the time-of-day most insensitive to pain. Also, dynamic tests and the mechanical pain model are not appropriate for detecting diurnal variability in pain. The results of this study may be partially explained by a potential analgesic effect of some hormones known to have diurnal variation (e.g., melatonin and cortisol).

Altered circadian patterns of salivary cortisol in low-functioning children and adolescents with autism

BACKGROUND

Reports of higher stress responsivity, altered sleep-wake cycle and a melatonin deficit in autism have stimulated interest in the cortisol circadian rhythm in individuals with autism.

METHODS

The study was conducted on 55 low-functioning children and adolescents with autism (11.3 ± 4.1 years-old) and 32 typically developing controls (11.7 ± 4.9 years-old) matched for age, sex and puberty. Behavioral assessment was performed using the Autism Diagnostic Observation Schedule (ADOS). Salivary samples for measurement of cortisol were collected during a 24-h period (at least 0800 h-Day 1, 1600 h, 0800 h-Day 2 for 46 individuals with autism and 27 controls, and 0800 h-Day 1, 1100 h, 1600 h, 2400 h, 0800 h-Day 2 for 13 individuals with autism and 20 controls). Overnight (2000 h-0800 h) urinary cortisol excretion was also measured.

RESULTS

The autism group displayed significantly higher levels of salivary cortisol at all time-points, flatter daytime and nighttime slopes, higher 0800 h cortisol levels on Day 2 compared to Day 1, and greater variances of salivary and urinary cortisol. There was a significant relationship between salivary cortisol levels and impairments in social interaction and verbal language. Overnight urinary cortisol excretion was similar in the autism and control groups.

CONCLUSION

Anticipation of the stressful collection procedure appears to contribute to the higher 0800 h-Day 2 versus 0800 h-Day 1 salivary cortisol levels in autism. This sensitization to stressors might be as, or even more, important clinically than exposure to novelty in autism. The similar group means for overnight urinary cortisol excretion indicate that basal HPA axis functioning is unaltered in low-functioning autism. The elevated salivary cortisol levels observed in autism over the 24-h period in a repeated stressful condition, flattened diurnal cortisol patterns and the apparent effect of anticipation are consistent with prior findings in high trait anxiety.

Influence of electric, magnetic, and electromagnetic fields on the circadian system: current stage of knowledge

One of the side effects of each electrical device work is the electromagnetic field generated near its workplace. All organisms, including humans, are exposed daily to the influence of different types of this field, characterized by various physical parameters. Therefore, it is important to accurately determine the effects of an electromagnetic field on the physiological and pathological processes occurring in cells, tissues, and organs. Numerous epidemiological and experimental data suggest that the extremely low frequency magnetic field generated by electrical transmission lines and electrically powered devices and the high frequencies electromagnetic radiation emitted by electronic devices have a potentially negative impact on the circadian system. On the other hand, several studies have found no influence of these fields on chronobiological parameters. According to the current state of knowledge, some previously proposed hypotheses, including one concerning the key role of melatonin secretion disruption in pathogenesis of electromagnetic field induced diseases, need to be revised. This paper reviews the data on the effect of electric, magnetic, and electromagnetic fields on melatonin and cortisol rhythms—two major markers of the circadian system as well as on sleep. It also provides the basic information about the nature, classification, parameters, and sources of these fields.

Circadian melatonin rhythm and excessive daytime sleepiness in Parkinson disease

IMPORTANCE

Diurnal fluctuations of motor and nonmotor symptoms and a high prevalence of sleep-wake disturbances in Parkinson disease (PD) suggest a role of the circadian system in the modulation of these symptoms. However, surprisingly little is known regarding circadian function in PD and whether circadian dysfunction is involved in the development of sleep-wake disturbances in PD.

OBJECTIVE

To determine the relationship between the timing and amplitude of the 24-hour melatonin rhythm, a marker of endogenous circadian rhythmicity, with self-reported sleep quality, the severity of daytime sleepiness, and disease metrics.

DESIGN, SETTING, AND PARTICIPANTS

A cross-sectional study from January 1, 2009, through December 31, 2012, of 20 patients with PD receiving stable dopaminergic therapy and 15 age-matched control participants. Both groups underwent blood sampling for the measurement of serum melatonin levels at 30-minute intervals for 24 hours under modified constant routine conditions at the Parkinson's Disease and Movement Disorders Center of Northwestern University.

INTERVENTIONS

Twenty-four hour monitoring of serum melatonin secretion.

MAIN OUTCOMES AND MEASURES

Clinical and demographic data, self-reported measures of sleep quality (Pittsburgh Sleep Quality Index) and daytime sleepiness (Epworth Sleepiness Scale), and circadian markers of the melatonin rhythm, including the amplitude, area under the curve (AUC), and phase of the 24-hour rhythm.

RESULTS

Patients with PD had blunted circadian rhythms of melatonin secretion compared with controls; the amplitude of the melatonin rhythm and the 24-hour AUC for circulating melatonin levels were significantly lower in PD patients (P < .001). Markers of the circadian phase were not significantly different between the 2 groups. Compared with PD patients without excessive daytime sleepiness, patients with excessive daytime sleepiness (Epworth Sleepiness Scale score ≥10) had a significantly lower amplitude of the melatonin rhythm and 24-hour melatonin AUC (P = .001). Disease duration, Unified Parkinson's Disease Rating Scale scores, levodopa equivalent dose, and global Pittsburgh Sleep Quality Index score in the PD group were not significantly related to measures of the melatonin circadian rhythm.

CONCLUSIONS AND RELEVANCE

Circadian dysfunction may underlie excessive sleepiness in PD. The nature of this association needs to be explored further in longitudinal studies. Approaches aimed to strengthen circadian function, such as timed exposure to bright light and exercise, might serve as complementary therapies for the nonmotor manifestations of PD.

Integration of biological clocks and rhythms

Animals, plants, and microorganisms exhibit numerous biological rhythms that are generated by numerous biological clocks. This article summarizes experimental data pertinent to the often-ignored issue of integration of multiple rhythms. Five contexts of integration are discussed: (i) integration of circadian rhythms of multiple processes within an individual organism, (ii) integration of biological rhythms operating in different time scales (such as tidal, daily, and seasonal), (iii) integration of rhythms across multiple species, (iv) integration of rhythms of different members of a species, and (v) integration of rhythmicity and physiological homeostasis. Understanding of these multiple rhythmic interactions is an important first step in the eventual thorough understanding of how organisms arrange their vital functions temporally within and without their bodies.

The effects of extremely low-frequency magnetic fields on melatonin and cortisol, two marker rhythms of the circadian system

In the past 30 years the concern that daily exposure to extremely low-frequency magnetic fields (ELF-EMF) (1 to 300 Hz) might be harmful to human health (cancer, neurobehavioral disturbances, etc) has been the object of debate, and has become a public health concern. This has resulted in the classification of ELF-EMF into category 2B, ie, agents that are “possibly carcinogenic to humans” by the International Agency for Research on Cancer. Since melatonin, a neurohormone secreted by the pineal gland, has been shown to possess oncostatic properties, a “melatonin hypothesis” has been raised, stating that exposure to EMF might decrease melatonin production and therefore might promote the development of breast cancer in humans. Data from the literature reviewed here are contradictory. In addition, we have demonstrated a lack of effect of ELF-EMF on melatonin secretion in humans exposed to EMF (up to 20 years' exposure) which rebuts the melatonin hypothesis. Currently, the debate concerns the effects of ELF-EMF on the risk of childhood leukemia in children chronically exposed to more than 0.4 μT. Further research is thus needed to obtain more definite answers regarding the potential deleterious effects of ELF-EMF.

Circadian rhythms in acute intermittent porphyria--a pilot study

BACKGROUND

Acute intermittent porphyria (AIP) is an inherited disorder of haem synthesis wherein a partial deficiency of porphobilinogen (PBG) deaminase (PBGD) with other factors may give rise to biochemical and clinical manifestations of disease. The biochemical hallmarks of active AIP are relative hepatic haem deficiency and uncontrolled up-regulation of hepatic 5-aminolevulinic acid (ALA) synthase-1 (ALAS1) with over-production of ALA and PBG. The treatment of choice is intravenous haem, which restores the deficient regulatory haem pool of the liver and represses ALAS1. Recently, haem has been shown to influence circadian rhythms by controlling their negative feedback loops. We evaluated whether subjects with AIP exhibited an altered circadian profile.

MATERIALS AND METHODS

Over a 21-h period, we measured levels of serum cortisol, melatonin, ALA, PBG and mRNA levels (in peripheral blood mononuclear cells) of selected clock-controlled genes and genes involved in haem synthesis in 10 Caucasian (European-American) women who were either postmenopausal or had been receiving female hormone therapy, six of whom have AIP and four do not and are considered controls.

RESULTS

Four AIP subjects with biochemical activity exhibited higher levels of PBG and lower levels and dampened oscillation of serum cortisol, and a trend for lower levels of serum melatonin, than controls or AIP subjects without biochemical activity. Levels of clock-controlled gene mRNAs showed significant increases over baseline in all subjects at 5 a.m. and 11 p.m., whereas mRNA levels of ALAS1, ALAS2 and PBGD were increased only at 11 p.m. in subjects with active AIP.

CONCLUSIONS

This pilot study provides evidence for disturbances of circadian markers in women with active AIP that may trigger or sustain some common clinical features of AIP.

What is the best approach to tailoring hydrocortisone dose to meet patient needs in 2012?

Cortisol is an essential stress hormone and replacement with oral hydrocortisone is lifesaving in patients with adrenal insufficiency. Cortisol has a diurnal rhythm regulated by the central body clock and this rhythm is a metabolic signal for peripheral tissue clocks. Loss of cortisol rhythmicity is associated with fatigue, depression and insulin resistance. A general principle in endocrinology is to replace hormones to replicate physiological concentrations; however, the pharmacokinetics of oral immediate-release hydrocortisone make it impossible to fully mimic the cortisol rhythm and patients still have an increased morbidity and mortality despite replacement. Traditionally, physicians have replaced hydrocortisone with a total daily dose based on the diurnal 24-h cortisol production rate with hydrocortisone given twice or thrice daily, with the highest dose first thing in the morning. Monitoring treatment and dose titration has been much debated with some clinicians using cortisol day curves and others relying on clinical symptoms. The main challenge is that there is no established biomarker of cortisol activity. In addressing the clinical question, we have taken the view that an understanding of the cortisol circadian rhythm and hydrocortisone pharmacokinetics is essential when tailoring hydrocortisone dose. Using this approach, we have developed a thrice daily, weight-related, dosing regimen and a pharmacokinetic and clinical method to monitor treatment. Our argument for replicating the cortisol circadian rhythm is based on the observation that disruption of the rhythm is associated with ill health, and the few studies that have compared different treatment regimens. Further studies are required to definitively test the benefits of replacing the cortisol circadian rhythm in patients with adrenal insufficiency.

24-hour intraocular pressure and ocular perfusion pressure in glaucoma

This review analyzes the currently available literature on circadian rhythms of intraocular pressure (IOP), blood pressure, and calculated ocular perfusion pressure (OPP) in patients with open-angle glaucoma. Although adequately powered, prospective trials are not available. The existing evidence suggests that high 24-hour IOP and OPP fluctuations can have detrimental effects in eyes with glaucoma. The currently emerging continuous IOP monitoring technologies may soon offer important contributions to the study of IOP rhythms. Once telemetric technologies become validated and widely available for clinical use, they may provide an important tool towards a better understanding of long- and short-term IOP fluctuations during a patient's daily routine. Important issues that need to be investigated further include the identification of appropriate surrogate measures of IOP and OPP fluctuation for patients unable to undergo 24-hour measurements, the determination of formulae that best describe the relationship between systemic blood pressure and IOP with OPP, and the exact clinical relevance of IOP and OPP fluctuation in individual patients. Despite the unanswered questions, a significant body of literature suggests that OPP assessment may be clinically relevant in a significant number of glaucoma patients.

Identification of human plasma metabolites exhibiting time-of-day variation using an untargeted liquid chromatography-mass spectrometry metabolomic approach

Although daily rhythms regulate multiple aspects of human physiology, rhythmic control of the metabolome remains poorly understood. The primary objective of this proof-of-concept study was identification of metabolites in human plasma that exhibit significant 24-h variation. This was assessed via an untargeted metabolomic approach using liquid chromatography–mass spectrometry (LC-MS). Eight lean, healthy, and unmedicated men, mean age 53.6 (SD ± 6.0) yrs, maintained a fixed sleep/wake schedule and dietary regime for 1 wk at home prior to an adaptation night and followed by a 25-h experimental session in the laboratory where the light/dark cycle, sleep/wake, posture, and calorific intake were strictly controlled. Plasma samples from each individual at selected time points were prepared using liquid-phase extraction followed by reverse-phase LC coupled to quadrupole time-of-flight MS analysis in positive ionization mode. Time-of-day variation in the metabolites was screened for using orthogonal partial least square discrimination between selected time points of 10:00 vs. 22:00 h, 16:00 vs. 04:00 h, and 07:00 (d 1) vs. 16:00 h, as well as repeated-measures analysis of variance with time as an independent variable. Subsequently, cosinor analysis was performed on all the sampled time points across the 24-h day to assess for significant daily variation. In this study, analytical variability, assessed using known internal standards, was low with coefficients of variation <10%. A total of 1069 metabolite features were detected and 203 (19%) showed significant time-of-day variation. Of these, 34 metabolites were identified using a combination of accurate mass, tandem MS, and online database searches. These metabolites include corticosteroids, bilirubin, amino acids, acylcarnitines, and phospholipids; of note, the magnitude of the 24-h variation of these identified metabolites was large, with the mean ratio of oscillation range over MESOR (24-h time series mean) of 65% (95% confidence interval [CI]: 49–81%). Importantly, several of these human plasma metabolites, including specific acylcarnitines and phospholipids, were hitherto not known to be 24-h variant. These findings represent an important baseline and will be useful in guiding the design and interpretation of future metabolite-based studies. (Author correspondence: Jooern.Ang@icr.ac.uk or Florence.Raynaud@icr.ac.uk)

Melatonin treatment effects on adolescent students' sleep timing and sleepiness in a placebo-controlled crossover study

During the last few decades, the incidence of sleep-onset insomnia, due to delay of circadian phase, has increased substantially among adolescents all over the world. We wanted to investigate whether a small dose of melatonin given daily, administered in the afternoon, could advance the sleep timing in teenagers. Twenty-one students, aged 14-19 yrs, with sleep-onset difficulties during school weeks were recruited. The study was a randomized, double blind, placebo (PL)-controlled crossover trial, lasting 5 wks. During the first 6 d in wks 2 and 4, the students received either PL or melatonin (1 mg) capsules between 16:30 and 18:00 h. During the first 6 d of wk 5, all students received melatonin. Wks 1 and 3 were capsule-free. In the last evening of each week and the following morning, the students produced saliva samples at home for later melatonin analysis. The samples were produced the same time each week, as late as possible in the evening and as early as possible in the morning. Both the student and one parent received automatic mobile text messages 15 min before saliva sampling times and capsule intake at agreed times. Diaries with registration of presumed sleep, subjective sleepiness during the day (Karolinska Sleepiness Scale, KSS) and times for capsule intake and saliva samplings were completed each day. Primary analysis over 5 wks gave significant results for melatonin, sleep and KSS. Post hoc analysis showed that reported sleep-onset times were advanced after melatonin school weeks compared with PL school weeks (p < .005) and that sleep length was longer (p < .05). After the last melatonin school week, the students fell asleep 68 min earlier and slept 62 min longer each night compared with the baseline week. Morning melatonin values in saliva diminished compared with PL (p < .001) and evening values increased (p < .001), indicating a possible sleep phase advance. Compared with PL school weeks, the students reported less wake up (p < .05), less school daytime sleepiness (p < .05) and increased evening sleepiness (p < .005) during melatonin weeks. We conclude that a small dose of melatonin given daily, administered in the afternoon, could advance the sleep timing and make the students more alert during school days even if they continued their often irregular sleep habits during weekends.

PER1 modulates SGLT1 transcription in vitro independent of E-box status

BACKGROUND AND AIMS

The intestine demonstrates profound circadian rhythmicity in glucose absorption in rodents, mediated entirely by rhythmicity in the transcription, translation, and function of the sodium glucose co-transporter SGLT1 (Slc5a1). Clock genes are rhythmic in the intestine and have been implicated in the regulation of rhythmicity of other intestinal genes; however, their role in the regulation of SGLT1 is unknown. We investigated the effects of one clock gene, PER1, on SGLT1 transcription in vitro.

METHODS

Caco-2 cells were stably transfected with knockdown vectors for PER1 and mRNA expression of clock genes and SGLT1 determined using quantitative polymerase chain reaction (qPCR). Chinese hamster ovary (CHO) cells were transiently cotransfected with combinations of the PER1 expression vectors and the wild-type SGLT1-luciferase promoter construct or the promoter with mutated E-box sequences.

RESULTS

Knockdown of PER1 increased native SGLT1 expression in Caco-2 enterocytes, while promoter studies confirmed that the inhibitory activity of PER1 on SGLT1 occurs via the proximal 1 kb of the SGLT1 promoter. E-box sites exerted a suppressive effect on the SGLT1 promoter; however, mutation of E-boxes had little effect on the inhibitory activity of PER1 on the SGLT1 promoter suggesting that the actions of PER1 on SGLT1 are independent of E-boxes.

CONCLUSIONS

Our findings suggest that PER1 exerts an indirect suppressive effect on SGLT1, possibly acting via other clock-controlled genes binding to non-E-box sites on the SGLT1 promoter. Understanding the regulation of rhythmicity of SGLT1 may lead to new treatments for the modulation of SGLT1 expression in conditions such as malabsorption, diabetes, and obesity.

Theoretical aspects of autism: biomarkers--a review

Autism is dramatically increasing in incidence and is now considered an epidemic. There are no objective means to diagnose the disorder. Diagnosis is made subjectively, based on the perceived behavior of the subject. This review presents an approach toward development of an objective measure of autism. Covering the literature from 1943 to the present in the PubMed and Ovid Medline databases, this review summarizes evidence of hormones, metabolites, amino acids, and other biomarkers present in significantly different quantities in autistic subjects compared to age- and sex-matched controls. These differences can be measured in the gastrointestinal, immunologic, neurologic, and toxicologic systems of the body, with some biomarkers showing ubiquitous application. In addition, there are unifying concepts, i.e., increased vulnerability to oxidative stress, immune glutamatergic dysfunction, and pineal gland malfunction. The variances of the biomarkers from the norm present the opportunity to create biomarker arrays that when properly developed and analyzed could result in an objective diagnosis with a ranking of the severity of autism for each subject. The contribution of each biomarker to the overall diagnosis could be calculated, thus providing a profile pattern unique to the individual. This profile could consequently provide information for therapeutic interventions on an individual basis.

The normalization of the cortisol awakening response and of the cortisol shift profile across consecutive night shifts--an experimental study

This study tested the hypothesis that the cortisol awakening response (CAR) and the cortisol shift profile normalize with successive night shifts due to the shift of the circadian system. 18 students (9 women, 9 men, 19-29 years), worked first four consecutive morning- and then four consecutive night shifts. Each work shift was preceded by an 8-h sleep opportunity meaning that the sleep-activity cycle was advanced by 8 h. The advance of the circadian system was promoted by a 2-h bright light pulse at the end of each night shift and quantified by 24-h phase assessment procedures (PA) before and after the four day shifts and again after the four night shifts. Saliva samples were taken 0, 15, 30, 45, and 60 min post-awakening, hourly during each work shift and each PA. During the night shift sequence, the CAR, indicated by the area under curve with respect to increase (AUC(I)), increased gradually across the 4-day sleep periods. Baseline levels were reached after 3 days in men and 4 days in women. The increase of the CAR was associated with a gradually increasing decline of cortisol levels during the night shifts. This adjustment was--at least not only--related to the advance of the circadian system which was 5 h. A contributor to the increase of the CAR might be the anticipation of the upcoming demands of the following work shifts.

Replication of cortisol circadian rhythm: new advances in hydrocortisone replacement therapy

Cortisol has one of the most distinct and fascinating circadian rhythms in human physiology. This is regulated by the central clock located in the suprachiasmatic nucleus of the hypothalamus. It has been suggested that cortisol acts as a secondary messenger between central and peripheral clocks, hence its importance in the synchronization of body circadian rhythms. Conventional immediate-release hydrocortisone, either at twice- or thrice-daily doses, is not capable of replicating physiological cortisol circadian rhythm and patients with adrenal insufficiency or congenital adrenal hyperplasia still suffer from a poor quality of life and increased mortality. Novel treatments for replacement therapy are therefore essential. Proof-of-concept studies using hydrocortisone infusions suggest that the circadian delivery of hydrocortisone may improve biochemical control and life quality in patients lacking cortisol with an impaired cortisol rhythm. Recently oral formulations of modified-release hydrocortisone are being developed and it has been shown that it is possible to replicate cortisol circadian rhythm and also achieve better control of morning androgen levels. These new drug therapies are promising and potentially offer a more effective treatment with less adverse effects. Definite improvements clearly need to be established in future clinical trials.

Hormones, nicotine, and cocaine: clinical studies

Nicotine and cocaine each stimulate hypothalamic-pituitary-adrenal and -gonadal axis hormones, and there is increasing evidence that the hormonal milieu may modulate the abuse-related effects of these drugs. This review summarizes some clinical studies of the acute effects of cigarette smoking or IV cocaine on plasma drug and hormone levels and subjective effects ratings. The temporal covariance between these dependent measures was assessed with a rapid (2 min) sampling procedure in nicotine-dependent volunteers or current cocaine users. Cigarette smoking and IV cocaine each stimulated a rapid increase in LH and ACTH, followed by gradual increases in cortisol and DHEA. Positive subjective effects ratings increased immediately after initiation of cigarette smoking or IV cocaine administration. However, in contrast to cocaine's sustained positive effects (<20 min), ratings of "high" and "rush" began to decrease within one or two puffs of a high-nicotine cigarette while nicotine levels were increasing. Peak nicotine levels increased progressively after each of three successive cigarettes smoked at 60 min intervals, but the magnitude of the subjective effects ratings and peak ACTH and cortisol levels diminished. Only DHEA increased consistently after successive cigarettes. The possible influence of neuroactive hormones on nicotine dependence and cocaine abuse and the implications for treatment of these addictive disorders are discussed.

Restricted feeding phase shifts clock gene and sodium glucose cotransporter 1 (SGLT1) expression in rats

The intestine exhibits striking diurnal rhythmicity in glucose uptake, mediated by the sodium glucose cotransporter (SGLT1); however, regulatory pathways for these rhythms remain incompletely characterized. We hypothesized that SGLT1 rhythmicity is linked to the circadian clock. To investigate this, we examined rhythmicity of Sglt1 and individual clock genes in rats that consumed food ad libitum (AL). We further compared phase shifts of Sglt1 and clock genes in a second group of rats following restricted feeding to either the dark (DF) or light (LF) phase. Rats fed during the DF were pair-fed to rats fed during the LF. Jejunal mucosa was harvested across the diurnal period to generate expression profiles of Sglt1 and clock genes Clock, Bmal1 (brain-muscle Arnt-like 1), ReverbA/B, Per(Period) 1/2, and Cry (Cryptochrome) 1/2. All clock genes were rhythmic in AL rats (P < 0.05). Sglt1 also exhibited diurnal rhythmicity, with peak expression preceding nutrient arrival (P < 0.05). Light-restricted feeding shifted the expression rhythms of Sglt1 and most clock genes (Bmal1, ReverbA and B, Per1, Per2, and Cry1) compared with dark-restricted feeding (P < 0.05). The Sglt1 rhythm shifted in parallel with rhythms of Per1 and ReverbB. These effects of restricted feeding highlight luminal nutrients as a key Zeitgeber in the intestine, capable of simultaneously shifting the phases of transporter and clock gene expression, and suggest a role for clock genes in regulating Sglt1 and therefore glucose uptake. Understanding the regulatory cues governing rhythms in intestinal function may allow new therapeutic options for conditions of dysregulated absorption such as diabetes and obesity.

Estimating trace deposition time with circadian biomarkers: a prospective and versatile tool for crime scene reconstruction

Linking biological samples found at a crime scene with the actual crime event represents the most important aspect of forensic investigation, together with the identification of the sample donor. While DNA profiling is well established for donor identification, no reliable methods exist for timing forensic samples. Here, we provide for the first time a biochemical approach for determining deposition time of human traces. Using commercial enzyme-linked immunosorbent assays we showed that the characteristic 24-h profiles of two circadian hormones, melatonin (concentration peak at late night) and cortisol (peak in the morning) can be reproduced from small samples of whole blood and saliva. We further demonstrated by analyzing small stains dried and stored up to 4 weeks the in vitro stability of melatonin, whereas for cortisol a statistically significant decay with storage time was observed, although the hormone was still reliably detectable in 4-week-old samples. Finally, we showed that the total protein concentration, also assessed using a commercial assay, can be used for normalization of hormone signals in blood, but less so in saliva. Our data thus demonstrate that estimating normalized concentrations of melatonin and cortisol represents a prospective approach for determining deposition time of biological trace samples, at least from blood, with promising expectations for forensic applications. In the broader context, our study opens up a new field of circadian biomarkers for deposition timing of forensic traces; future studies using other circadian biomarkers may reveal if the time range offered by the two hormones studied here can be specified more exactly.

Duration of suppression of adrenal steroids after glucocorticoid administration

Hydrocortisone has long been the treatment of choice for congenital adrenal hyperplasia (CAH). However, treatment with this medication remains problematic. Patients with 21-hydroxylase deficiency CAH have significant diurnal variation in the secretion of 17-hydroxyprogesterone (17OHP). When considering treatment strategies, this variation must be considered along with the pharmacokinetic and pharmacodynamic properties of exogenous glucocorticoids. Orally administered hydrocortisone is highly bioavailable, but it has a short time to maximum concentration (T_max) and half life (T_1/2). While prednisone has a somewhat longer T_max and T_1/2, they remain relatively short. There have been several studies of the pharmacodynamics of hydrocortisone. We present data indicating that the maximum effect of hydrocortisone in CAH patients is seen 3 hours after a morning dose. After an evening dose, suppression of adrenal hormones continues until approximately 0500 the next day. In both situations, however, there is a large degree of intersubject variability. These data are consistent with earlier published studies. Use of alternate specimen types, possibly in conjunction with delayed release hydrocortisone preparations under development, may allow the practitioner to design a medication regimen that provides improved control of androgen secretion. Whatever dosing strategy is used, clinical judgment is required to ensure the best outcome.

Reproducibility of plasma and urine biomarkers among premenopausal and postmenopausal women from the Nurses' Health Studies

BACKGROUND

Temporal variability of biomarkers should be evaluated before their use in epidemiologic studies.

METHODS

We evaluated the reproducibility, using intraclass correlation coefficients (ICC), of 77 plasma and 9 urinary biomarkers over 1 to 3 years among premenopausal (n = 40) and postmenopausal (n = 35-70) participants from the Nurses' Health Study and Nurses' Health Study II.

RESULTS

Plasma and urinary stress hormones and melatonin were measured among premenopausal women, whereas melatonin and the remaining biomarkers were measured in postmenopausal women. ICCs were good to excellent for plasma carotenoids (0.73-0.88), vitamin D analytes (0.56-0.72), bioactive somatolactogens (0.62), soluble leptin receptor (0.82), resistin (0.74), and postmenopausal melatonin (0.63). Reproducibility was lower for some of the plasma fatty acids (0.38-0.72), matrix metalloproteinases (0.07-0.91), and premenopausal melatonin (0.44). The ICCs for plasma and urinary phytoestrogens were poor (< or = 0.09) except for enterolactone (plasma, 0.44; urinary, 0.52). ICCs for the stress hormones among premenopausal women ranged from 0 (plasma cortisol) to 0.45 (urinary dopamine).

CONCLUSIONS

Our results indicate that for the majority of these markers, a single measurement can reliably estimate average levels over a 1- to 3-year period in epidemiologic studies. For analytes with fair to good ICCs, reproducibility data can be used for measurement error correction. Analytes with poor ICCs should only be used in settings with multiple samples per subject or in populations in which ICCs are higher.

IMPACT

This article summarizes the feasibility of the use of >80 biomarkers in epidemiologic studies in which only one biospecimen is available to represent longer term exposure.