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

Br J Clin Pharmacol. 2016 Sep;82(3):706-16. doi: 10.1111/bcp.13007. Epub 2016 Jun 3.


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: NCT02324452.

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

MeSH terms

  • Adult
  • Circadian Rhythm*
  • Dihydrouracil Dehydrogenase (NADP) / genetics
  • Dihydrouracil Dehydrogenase (NADP) / metabolism*
  • Female
  • Gene Expression / genetics
  • Healthy Volunteers
  • Humans
  • Leukocytes, Mononuclear / enzymology*
  • Male
  • Middle Aged
  • Plasma / enzymology*
  • Polymorphism, Genetic / genetics
  • Thymidylate Synthase / genetics
  • Thymidylate Synthase / metabolism*
  • Uracil / analogs & derivatives
  • Uracil / blood
  • Young Adult


  • dihydrouracil
  • Uracil
  • Dihydrouracil Dehydrogenase (NADP)
  • Thymidylate Synthase

Associated data

  • NTR/NTR4639