Circadian rhythms in medicine

Chronopharmacokinetics of drugs in toxicological aspects: A short review for pharmacy practitioners

A rough 24-hour cycle driven endogenously in biochemical, physiological or behavioral processes is called circadian rhythm. Chronobiology is the study of biological temporal rhythms. For decades, we know that the biological rhythm and the drug metabolism are also affected from daylight and chronopharmacology became recognized by scientists in the early 1970s. Its lateral branch chronocopharmacokinetics is the study of rhythmic, predictable-in-time differences in the pharmacokinetics of drugs. Chronopharmacokinetic studies are performed at every step of the biotransformation i.e., absorption, distribution, metabolism and excretion. Feeding schedules, sex and phenotype must be taken into consideration while applying pharmacotherapy to increase the efficiency and to decrease side effects. The impact of drugs on circadian rhythm should be not neglected. On the other hand, new special drug delivery systems can be used to synchronize drug concentrations according to circadian rhythms. “Chronopharmaceuticals” can identify the proper dosing time and this amelioration will lead to improved progress and diffusion of pharmacotherapy. Chronopharmaceuticals coupled with nanotechnology could be the future of drug delivery systems, and lead to safer and more efficient disease therapy in the future. In this review, we will discuss the pharmacokinetic effects of circadian rhythm and its toxicological outcomes. Besides, we will try to give some practical points for clinical pharmacist/pharmacy practitioners, concerning chronopharmacokinetics.

Jet lag: therapeutic use of melatonin and possible application of melatonin analogs

Each year millions of travelers undertake long distance flights over one or more continents. These multiple time zone flights produce a constellation of symptoms known as jet lag. Familiar to almost every intercontinental traveler is the experience of fatigue upon arrival in a new time zone, but almost as problematic are a number of other jet lag symptoms. These include reduced alertness, nighttime insomnia, loss of appetite, depressed mood, poor psychomotor coordination and reduced cognitive skills, all symptoms which are closely affected by both the length and direction of travel. The most important jet lag symptoms are due to disruptions to the body's sleep/wake cycle. Clinical and pathophysiological studies also indicate that jet lag can exacerbate existing affective disorders. It has been suggested that dysregulation of melatonin secretion and occurrence of circadian rhythm disturbances may be the common links which underlie jet lag and affective disorders. Largely because of its regulatory effects on the circadian system, melatonin has proven to be highly effective for treating the range of symptoms that accompany transmeridian air travel. Additionally, it has been found to be of value in treating mood disorders like seasonal affective disorder. Melatonin acts on MT(1) and MT(2) melatonin receptors located in the hypothalamic suprachiasmatic nuclei, the site of the body's master circadian clock. Melatonin resets disturbed circadian rhythms and promotes sleep in jet lag and other circadian rhythm sleep disorders, including delayed sleep phase syndrome and shift-work disorder. Although post-flight melatonin administration works efficiently in transmeridian flights across less than 7-8 times zones, in the case longer distances, melatonin should be given by 2-3 days in advance to the flight. To deal with the unwanted side effects which usually accompany this pre-departure treatment (acute soporific and sedative effects in times that may not be wanted), the suppression of circadian rhythmicity by covering symmetrically the phase delay and the phase advance portions of the phase response curve for light, together with the administration of melatonin at local bedtime to resynchronize the circadian oscillator, have been proposed. The current view that sleep loss is a major cause of jet lag has focused interest on two recently developed pharmacological agents. Ramelteon and agomelatine are melatonin receptor agonists which, compared to melatonin itself, have a longer half-life and greater affinity for melatonin receptors and consequently are thought to hold promise for treating a variety of circadian disruptions.

Variability of preoperatively determined hepatic volumes in potential living liver donors

RATIONALE AND OBJECTIVES

The aim of the study is to evaluate variability in hepatic volumes during the preoperative period in potential liver donors.

MATERIALS AND METHODS

Eight potential living liver donors underwent preoperative multirow-detector computed tomographic assessment of hepatic transplant volumes twice. Intraindividual delay between the two examinations range was 3-62 days (mean, 30.1 days). Liver volumes were determined in a blinded fashion by an experienced radiologist and a transplantation surgeon. Results were compared and correlated with time of data acquisition during the day.

RESULTS

Interobserver variability for assessments of liver volumes range was 6-32 mL (mean, 16 mL). Intraindividually, the difference between the two volume assessments ranged between -103 and +45 mL (mean, -19 mL), corresponding to percentages of alteration between -7.5% and +3.2%. There was no statistical correlation evident concerning volume alterations and specific time of data acquisition.

CONCLUSION

Neither time of data acquisition nor waiting period for the surgical procedure seems to affect the accuracy of liver volume calculation. Apparent volume variations likely are in the range of the method error of the applied technique.

Timing is everything: does the robust upregulation of noradrenergically regulated plasticity genes underlie the rapid antidepressant effects of sleep deprivation?

The mechanisms by which sleep deprivation brings about rapid antidepressant effects remain to be elucidated. Biological rhythms have the capacity to temporally dissociate biochemical processes, and imposing a temporal coincidence on normally dissociated events can have striking and unexpected effects. In this context, it is noteworthy that the locus coeruleus (LC) noradrenergic projection is quiescent only during rapid-eye-movement (REM) sleep, when the target tissues display their greatest sensitivity; indeed, the temporal dissociation between the firing of the LC noradrenergic neurons and the sensitivity of its postsynaptic targets in the cortex may have considerable relevance for the antidepressant effects of sleep deprivation. Sleep deprivation rapidly upregulates several plasticity-related genes, effects that are noradrenergically mediated; these are the very same genes that are upregulated by chronic antidepressants. Thus, activating the norepinephrine system during REM sleep (by infusing an alpha(2) antagonist) may allow an interaction with a primed, sensitized postsynaptic milieu, thereby rapidly increasing the expression of plasticity genes and consequently a rapid antidepressant response.