Toxicokinetics of tremorogenic natural products, harmane and harmine, in male Sprague-Dawley rats

Abstract

Tremorogenic beta-carboline alkaloids are present in foodstuffs and beverages. Acute exposure to beta-carboline derivatives causes severe tremor; however, the disposition of these dietary contaminants remains unclear. This study was performed to evaluate toxicokinetics of harmane and harmine, two major beta-carboline alkaloids, in rats. Blood concentrations of both toxicants were quantified by high-performance liquid chromatography (HPLC). Following an intravenous injection (0.5 mg/kg), the concentration-time profiles of harmane or harmine fit well with a two-compartment model. While both compounds had comparable elimination t 1/2beta (24 and 26 min for harmane and harmine, respectively), the systemic clearance (CLs) for harmine (103.2 ml/kg/ml) was two times greater than that for harmane (52.2 ml/kg/ml). Accordingly, the area under the blood concentration-time curve (AUC) in harmane-treated rats was 2.7-fold greater than that in harmine-treated rats. Harmine appeared to distribute to tissues better than harmane, with a larger volume of distribution (V,d) (3.9 and 1.6 L/kg for harmine and harmane, respectively). After an oral dose (20 mg/kg), the absolute bioavailability (F) was 19% for harmane and 3% for harmine. Harmane was absorbed more slowly (lower Ka), yet more completely (higher Cmax' AUC, and F) than harmine. An oral administration of harmane resulted in blood harmine whose formation accounted for 13% of the ingested harmane, indicating a biotransformation of harmane to harmine. These results suggest that harmane is absorbed into the systemic circulation more completely than harmine. Upon entering the body, harmane can be metabolized to form harmine; the latter may better distribute to the tissue compartment.

FIGURE 1

Blood concentration–time profiles of harmane or harmine in male Sprague-Dawley rats following an iv administration of 0.5 mg/kg of either harmane or harmine. Blood concentrations of harmane and harmine were determined by HPLC after sample extraction. The lines indicate the best fit of a two-compartment model with first-order elimination from the central compartment to the observed data: (A) harmane in rat blood (n = 4); (B) harmine in rat blood (n = 4).

FIGURE 2

Blood concentration–time profiles of harmane or harmine in male Sprague-Dawley rats following a single oral dose of either harmane or harmine at 20 mg/kg by oral gavage in corn oil. Blood concentrations of harmane and harmine were determined by HPLC after sample extraction. The lines indicate the best fit of a one-compartment model with first-order absorption to the observed data: (A) harmane in rat blood (n = 3); (B) harmine in rat blood (n = 5).

FIGURE 3

A typical HPLC chromatogram of harmane and its metabolite harmine in rat blood following a single oral dose of harmane (20 mg/kg). The data represent a 10-min blood sample collected from rat 1.

FIGURE 4

Blood concentration–time profiles of harmane (parent compound) and harmine (metabolite) of rat 1 following a single oral dose of harmane at 20 mg/kg by gavage.

FIGURE 5

Proposed metabolic pathway for harmane and harmine. Harmane, upon being absorbed, undergoes first-pass metabolism by the liver cytochrome P-450 system to produce the 7-hydroxyl metabolite, which is further methylated to form harmine. A portion of harmine enters the blood circulation as shown in Figures 3 and 4, while the other portion of harmine is hydroxylated by P-450 enzyme.