Quantification of metabolite cinnamic acid of cinnamon (Cinnamomum zeylanicum) in human plasma

Cinnamomum zeylanicum (CZ) is known to have numerous beneficial medicinal effects. The mechanism of action and compounds which account for these effects are not yet clearly defined. The present study aims to develop and validate a method to quantify the metabolites of CZ in human plasma and study its pharmacokinetic profile. Cinnamic acid (CA) was identified as the main metabolites of CZ in human plasma and was used to develop and validate the method.  HPLC with a UV-detector was used to identify and quantify CA. Linearity, precision, bias, repeatability, and lower limit of detection (LOD) were determined. CZ (5 g) was orally administered to 5 healthy volunteers and serial blood samples were taken, to determine maximal plasma concentration (C_max), time to reach maximal concentration (T_max) and elimination half-life (T_½) of CA. The precision, bias, and repeatability, of the method were 7.73%, 4.20%, and 5.63%, respectively. LOD was 1.11 µmol/L and samples were stable up to five days at 4 ^oC. Recovery of the method was 95% -125%. The retention time of CA was 16 minutes at 254 nm. Concentrations of CA between 0.5 and 200.0 µmol/L in a plasma matrix showed a linear response. C_max was 1.9 ± 1.5 μmol/L, while T_max and T_½ were 15 and 36 minutes respectively. The study developed a sensitive and specific HPLC method to detect CA, a key metabolite of CZ in humans, which is suitable for human pharmacokinetic studies. These pharmacokinetic parameters (C_max, T_max, T_½) would help in further development of CZ as a pharmaceutical agent for use in humans.