Evaluation of the transport, in vitro metabolism and pharmacokinetics of Salvinorin A, a potent hallucinogen

Abstract

Salvinorin A is an unregulated potent hallucinogen isolated from the leaves of Salvia divinorum. It is the only known non-nitrogenous kappa-opioid selective agonist, and rivals synthetic lysergic acid diethylamide (LSD) in potency. The objective of this study was to characterize the in vitro transport, in vitro metabolism, and pharmacokinetic properties of Salvinorin A. The transport characteristics of Salvinorin A were assessed using MDCK-MDR1 cell monolayers. The P-glycoprotein (P-gp) affinity status was assessed by the P-gp ATPase assay. In vitro metabolism studies were performed with various specific human CYP450 isoforms and UGT2B7 to assess the metabolic characteristics of Salvinorin A. Cohorts (n = 3) of male Sprague Dawley rats were used to evaluate the pharmacokinetics and brain distribution of Salvinorin A (10 mg/kg, intraperitoneal (i.p.) over a 240-min period. A validated UV-HPLC and LC/MS/MS method was used to quantify the hallucinogen concentrations obtained from the in vitro and in vivo studies, respectively. Salvinorin A displayed a high secretory transport in the MDCK-MDR1 cells (4.07 +/- 1.34 x 10(-)5 cm/s). Salvinorin A also stimulated the P-gp ATPase activity in a concentration (5 and 10 microM)-dependent manner, suggesting that it may be a substrate of (P-gp). A significant decrease in Salvinorin A concentration ranging from 14.7 +/- 0.80% to 31.1 +/- 1.20% was observed after incubation with CYP2D6, CYP1A1, CYP2C18, and CYP2E1, respectively. A significant decrease was also observed after incubation with UGT2B7. These results suggest that Salvinorin A maybe a substrate of UGT2B7, CYP2D6, CYP1A1, CYP2E1, and CYP2C18. The in vivo pharmacokinetic study showed a relatively fast elimination with a half-life (t1/2) of 75 min and a clearance (Cl/F) of 26 L/h/kg. The distribution was extensive (Vd of 47.1 L/kg); however, the brain to plasma ratio was 0.050. Accordingly, the brain half-life was relatively short, 36 min. Salvinorin A is rapidly eliminated after i.p. dosing, in accordance with its fast onset and short duration of action. Further, it appears to be a substrate for various oxidative enzymes and multi-drug resistant protein, P-gp.

Fig. 1

Chemical structure of Salvinorin A and B

Fig. 2

Salvinorin A in vitro metabolism screening with various CYP 450 isoforms. Salvinorin was incubated with CYP450 enzymes at a concentration of 50 μM (a), or 5 μM (b) as indicated. The values show the % reduction on initial concentration (mean ± SD, n=3). Different from initial concentration *p< 0.05 and **p< 0.01.

Fig. 3

Salvinorin A in vitro metabolism screening with UGT2B7 (n=3). Salvinorin was incubated with UGT2B7 at a concentration of 50, 10 and 5 μM as indicated. The values show the % reduction on initial concentration (mean ± SD, n=3). Different from initial concentration *p< 0.05 and **p< 0.01.

Fig. 4

Salvinorin A (a) plasma concentration versus time profile (b) brain concentration versus time profile. After a 10 mg/kg i.p. dose to Sprague Dawley rats (n =3/pt), (mean ± SD).