Chronobiology's progress. Part II, chronomics for an immediately applicable biomedicine

Applications of cosinor rhythmometry in pharmacology

Study design and data analysis are two important aspects relevant to chronopharmacometrics. Blunders can be avoided by recognizing that most physiological variables are circadian periodic. Both ill health and treatment can affect the amplitude, phase, and/or period of circadian (and other) rhythms, in addition to their mean. The involvement of clock genes in molecular pathways related to important physiological systems underlies the bidirectional relationship often seen between circadian rhythm disruption and disease risk. Circadian rhythm characteristics of marker rhythms interpreted in the light of chronobiologic reference values represent important diagnostic tools. A set of cosinor-related programs is presented. They include the least squares fit of multiple-frequency cosine functions to model the time structure of individual records; a cosinor-based spectral analysis to detect periodic signals; the population-mean cosinor to generalize inferences; the chronobiologic serial section to follow the time course of changing rhythm parameters over time; and parameter tests to assess differences among populations. Relative merits of other available cosinor and non-parametric algorithms are reviewed. Parameter tests to compare individual records and a self-starting cumulative sum (CUSUM) make personalized chronotherapy possible, where the treatment of each patient relies on an N-of-1 design. Methods are illustrated in a few examples relevant to endocrinology, cancer and cardiology. New sensing technology yielding large personal data sets is likely to change the healthcare system. Chronobiologic concepts and methods should become an integral part of these evolving systems.

Application of bioinformatics in chronobiology research

Bioinformatics and other well-established sciences, such as molecular biology, genetics, and biochemistry, provide a scientific approach for the analysis of data generated through “omics” projects that may be used in studies of chronobiology. The results of studies that apply these techniques demonstrate how they significantly aided the understanding of chronobiology. However, bioinformatics tools alone cannot eliminate the need for an understanding of the field of research or the data to be considered, nor can such tools replace analysts and researchers. It is often necessary to conduct an evaluation of the results of a data mining effort to determine the degree of reliability. To this end, familiarity with the field of investigation is necessary. It is evident that the knowledge that has been accumulated through chronobiology and the use of tools derived from bioinformatics has contributed to the recognition and understanding of the patterns and biological rhythms found in living organisms. The current work aims to develop new and important applications in the near future through chronobiology research.

Toward a personalized chronotherapy of high blood pressure and a circadian overswing

Timing can greatly affect the response to a stimulus, including antihypertensive medications. Herein, we assess the response of 30 patients to losartan/hydrochlorothiazide (L/H), administered for at least 1 month at a given circadian stage to each patient, this stage being changed during consecutive spans to cover six treatment times from awakening to bedtime at approximately 3-hour intervals. At the end of each stage, each patient underwent a 7-day around-the-clock ambulatory blood pressure (BP) profile, analyzed chronobiologically. A larger reduction of the midline estimating statistic of rhythm (MESOR; a rhythm-adjusted mean) of diastolic BP was achieved by L/H administration in the early morning for more patients (P < .05), while treatment upon awakening was the best choice for most patients to reduce the circadian amplitude of BP the most (P < .01). The optimal treatment time varied considerably among patients, however. Special attention should be given to the effect on the circadian amplitude since treatment can increase it above a threshold, beyond which there is a marked increase in cardiovascular disease risk. The results indicate the desirability to individualize the optimization of the antihypertensive effect of L/H by timing along the circadian scale.

Prehypertension in disease-free adults: a marker for an adverse cardiometabolic risk profile

Cardiovascular disease (CVD) is the leading cause of death worldwide. Understandably, cardiometabolic risk assessment is an integral component of every adult health evaluation. Customary assessment measures are, however, inadequate: as two-thirds of sudden cardiac deaths occur in clinically healthy individuals. Novel indicators favoring early recognition of adverse cardiometabolic risk in disease-free adults are clearly needed. Clinically healthy disease-free adults with prehypertension (PreHTN: BP120-139/80-89 mm Hg) have an adverse cardiometabolic risk profile. A statistical analysis of disease-free adult NHANES participants was conducted from 1999 to 2006. Overall prevalence of PreHTN in disease-free adults was 36.3%. Prevalence was higher in men (P<0.001) increasing with age up to 70 years (P<0.001). Prevalence correlated strongly with indicators of adverse cardiometabolic risk profile: it was higher with increasing body mass index (BMI) and waist circumference (WC) (P<0.001 for both). Means were significantly higher for BMI, WC, glucose, insulin, hemoglobin A1c, homeostasis model assessment, pulse pressure, C-reactive protein, total cholesterol and triglycerides in subjects with PreHTN (vs. desirable BP: P<0.05 for all). Prevalence of two or more unfavorable risk factors (other than high BP) was 30% higher in disease-free adults with PreHTN vs. desirable BP (prevalence ratio: 1.30; 95% CI: 1.22, 1.39). Detection of PreHTN (a precursor for subsequent HTN), during annual health maintenance in disease-free adults, (especially with one or more of the recognized CVD risk correlates), could become an early marker of adverse cardiometabolic risk profile. Clinical care designed to prevent progression from PreHTN to HTN (JNC 7 recommendation) may attenuate risk.

Prediabetes is associated with abnormal circadian blood pressure variability

Blood pressure (BP) exhibits a circadian variation characterized by a morning increase, followed by a small postprandial valley and a deeper descent during nocturnal rest. Although abnormal 24-h variability (abnormal circadian variability (ACV)) predicts adverse cardiovascular disease (CVD) outcomes, a 7-day automatic ambulatory BP monitoring (ABPM) and subsequent chronobiologic analysis of the gathered data, permits identification of consistency of any abnormal circadian variation. To test whether normal overweight healthy men and women with prediabetes differed from subjects with normoglycemia in having ACV with a 7-day ABPM. Consent for a 7-day ABPM was obtained from subjects with family history of diabetes mellitus, who were participating in the screening phase for a randomized, double blind, placebo-controlled weight loss trial in prediabetics to prevent progression to diabetes mellitus. The automatic 7-day ABPM device recorded BP and heart rate every 30 min during the day and every 60 min during the night. Normoglycemic and prediabetic subjects matched for age, sex, race, BP, BMI, waist circumference and glycemic control, differed statistically significantly only in their fasting and/or 2-h postprandial serum glucose concentrations. Chronobiologically-interpreted 7-day ABPM uncovered no abnormalities in normoglycemics, whereas prediabetics had a statistically significantly higher incidence of high mean BP (MESOR-hypertension), excessive pulse pressure and/or circadian hyper-amplitude-tension (CHAT) (P<0.001). ACV detected with 7-day ABPM may account for the enhanced CVD risk in prediabetes. These findings provide a basis for larger-scale studies to assess the predictive value of 7-day ABPM over the long term.