Pronounced between-subject and circadian variability in thymidylate synthase and dihydropyrimidine dehydrogenase enzyme activity in human volunteers

Abstract

Aims: The enzymatic activity of dihydropyrimidine dehydrogenase (DPD) and thymidylate synthase (TS) are important for the tolerability and efficacy of the fluoropyrimidine drugs. In the present study, we explored between-subject variability (BSV) and circadian rhythmicity in DPD and TS activity in human volunteers.

Methods: The BSVs in DPD activity (n = 20) in peripheral blood mononuclear cells (PBMCs) and in plasma, measured by means of the dihydrouracil (DHU) and uracil (U) plasma levels and DHU : U ratio (n = 40), and TS activity in PBMCs (n = 19), were examined. Samples were collected every 4 h throughout 1 day for assessment of circadian rhythmicity in DPD and TS activity in PBMCs (n = 12) and DHU : U plasma ratios (n = 23). In addition, the effects of genetic polymorphisms and gene expression on DPD and TS activity were explored.

Results: Population mean (± standard deviation) DPD activity in PBMCs and DHU : U plasma ratio were 9.2 (±2.1) nmol mg(-1) h(-1) and 10.6 (±2.4), respectively. Individual TS activity in PBMCs ranged from 0.024 nmol mg(-1) h(-1) to 0.596 nmol mg(-1) h(-1) . Circadian rhythmicity was demonstrated for all phenotype markers. Between 00:30 h and 02:00 h, DPD activity in PBMCs peaked, while the DHU : U plasma ratio and TS activity in PBMCs showed trough activity. Peak-to-trough ratios for DPD and TS activity in PBMCs were 1.69 and 1.62, respectively. For the DHU : U plasma ratio, the peak-to-trough ratio was 1.43.

Conclusions: BSV and circadian variability in DPD and TS activity were demonstrated. Circadian rhythmicity in DPD might be tissue dependent. The results suggested an influence of circadian rhythms on phenotype-guided fluoropyrimidine dosing and supported implications for chronotherapy with high-dose fluoropyrimidine administration during the night.

Trial registration: ClinicalTrials.gov NCT02324452.

Keywords: 5-fluorouracil; capecitabine; circadian rhythm; dihydropyrimidine dehydrogenase; thymidylate synthase.

© 2016 The British Pharmacological Society.

Figures

Figure 1

Intraday variability in dihydropyrimidine dehydrogenase (A) and thymidylate synthase activity (B) in peripheral blood mononuclear cells from volunteers (n = 12). Grey lines represent individual lines for DPD and TS activity. Mean ± standard error per time point are shown by black points and error bars. Differences between peak and trough activities are supported by P‐values. DPD, dihydropyrimidine dehydrogenase; PBMCs, peripheral blood mononuclear cells; TS, thymidylate synthase

Figure 2

Intraday variability in the dihydrouracil : uracil plasma ratio (A), uracil plasma levels (B) and dihydrouracil plasma levels (C) in 23 healthy volunteers. Grey solid lines represent individual curves. Mean ± standard error per time point is shown by black points and error bars. Differences between peak and trough levels are supported by P‐values. DHU, dihydrouracil; U, uracil

Figure 3

Visual predictive checks for final models for circadian rhythms in dihydropyrimidine dehydrogenase (A) and thymidylate synthase (B) activity in peripheral blood mononuclear cells, and uracil (C) and dihydrouracil (D) plasma levels. Lines represent the 10th percentile, median and 90th percentile of observed data. Shaded areas represent corresponding 95% confidence intervals of simulated data. DPD, dihydropyrimidine dehydrogenase; PBMCs, peripheral blood mononuclear cells; TS, thymidylate synthase

Figure 4

Typical patterns of circadian variability in dihydropyrimidine dehydrogenase and thymidylate synthase enzyme activity in peripheral blood mononuclear cells, and uracil and dihydrouracil plasma levels in healthy volunteers. Circadian variability is expressed as a percentage of the mesor (rhythm‐adjusted mean). DPD, dihydropyrimidine dehydrogenase; TS, thymidylate synthase. Uracil (ng ml−1), dihydrouracil (ng ml−1), DPD activity in PBMCs (nmol mg−1 h−1), TS activity in PBMCs (nmol mg−1 h−1)