In vivo-formed versus preformed metabolite kinetics of trans-resveratrol-3-sulfate and trans-resveratrol-3-glucuronide

Abstract

Metabolites in safety testing have gained a lot of attention recently. Regulatory agencies have suggested that the kinetics of preformed and in vivo-formed metabolites are comparable. This subject has been a topic of debate. We have compared the kinetics of in vivo-formed with preformed metabolites. trans-3,5,4'-Trihydroxystilbene [trans-resveratrol (RES)] and its two major metabolites, resveratrol-3-sulfate (R3S) and resveratrol-3-glucuronide (R3G) were used as model substrates. The pharmacokinetics (PK) of R3S and R3G were characterized under two situations. First, the pharmacokinetics of R3S and R3G were characterized (in vivo-formed metabolite) after administration of RES. Then, synthetic R3S and R3G were administered (preformed metabolite) and their pharmacokinetics were characterized. PK models were developed to describe the data. A three-compartment model for RES, a two-compartment model for R3S (preformed), and an enterohepatic cycling model for R3G (preformed) was found to describe the data well. These three models were further combined to build a comprehensive PK model, which was used to perform simulations to predict in vivo-formed metabolite kinetics. Comparisons were made between in vivo-formed and preformed metabolite kinetics. Marked differences were observed in the kinetics of preformed and in vivo-formed metabolites.

Fig. 1.

Structure of RES and its four monoconjugated metabolites, i.e., R3S, R4′S, R3G, and R4′G.

Fig. 2.

Mean plasma concentration-time profiles after administration of RES (15 mg/kg i.a.; A), R3S (5 mg/kg i.a.; B), and R3G (3.5 mg/kg i.a.; C). Data are presented as mean ± S.D., n = 4–5.

Fig. 3.

Compartmental modeling of RES, R3G, and R3S disposition. A, three-compartment PK model 1 describing the disposition of RES after administration of RES (15 mg/kg i.a.). V_c, volume of the central compartment; k, first-order rate constants for RES disposition. B, observed average RES concentration (data points) and PK model 1 predicted (solid line) RES concentration-time profiles after RES administration, and plot of weighted residuals versus predicted RES concentration (inset). C, two-compartment PK model 2 describing the disposition of R3S after administration of R3S (5 mg/kg i.a.). V_c,R3S, volume of the central compartment; k, first-order rate constants for R3S disposition. D, observed average R3S concentration (data points) and PK model 2 predicted (solid line) R3S concentration-time profiles after R3S administration, and plot of weighted residuals versus predicted R3S concentration (inset). E, enterohepatic cycling PK model 3 describing the disposition of R3G after administration of R3G (3.5 mg/kg i.a.). V_c,R3G, volume of the central compartment; k, first-order rate constants for R3G disposition. F, observed average R3G concentration (data points) and PK model 3 predicted (solid line) R3G concentration-time profiles after R3G administration, and plot of weighted residuals versus predicted R3G concentration (inset). [Note: The notation used throughout is k(from, to). In SAAM II software, the rate constants have a different notation k(to, from).]

Fig. 4.

PK model 4 describing the disposition of in vivo-formed metabolite R3S and R3G after RES (15 mg/kg i.a.) administration. Individual models for RES, R3S, and R3G are as described in Fig. 3. V_c, volumes of central compartments; k, first-order disposition rate constants; k_f, first-order formation rate constants for RES metabolites. [Note: The notation used throughout is k(from, to). In SAAM II software, the rate constants have a different notation k(to, from).]

Fig. 5.

Observed and PK model 4 simulated concentration-time profiles of RES (A), R3S (B), and R3G (C) after RES administration, assuming elimination clearance of preformed metabolites to be equal to in vivo-formed metabolites.

Fig. 6.

Observed and PK model 4 simulated concentration-time profiles of RES (A), R3S (B), and R3G (C) after RES administration, assuming elimination clearance of preformed metabolites to be not equal to in vivo-formed metabolites.