Intestinal Transport Characteristics and Metabolism of C-Glucosyl Dihydrochalcone, Aspalathin

Abstract

Insight into the mechanisms of intestinal transport and metabolism of aspalathin will provide important information for dose optimisation, in particular for studies using mouse models. Aspalathin transportation across the intestinal barrier (Caco-2 monolayer) tested at 1–150 µM had an apparent rate of permeability (Papp) typical of poorly absorbed compounds (1.73 × 10−6 cm/s). Major glucose transporters, sodium glucose linked transporter 1 (SGLT1) and glucose transporter 2 (GLUT2), and efflux protein (P-glycoprotein, PgP) (1.84 × 10−6 cm/s; efflux ratio: 1.1) were excluded as primary transporters, since the Papp of aspalathin was not affected by the presence of specific inhibitors. The Papp of aspalathin was also not affected by constituents of aspalathin-enriched rooibos extracts, but was affected by high glucose concentration (20.5 mM), which decreased the Papp value to 2.9 × 10−7 cm/s. Aspalathin metabolites (sulphated, glucuronidated and methylated) were found in mouse urine, but not in blood, following an oral dose of 50 mg/kg body weight of the pure compound. Sulphates were the predominant metabolites. These findings suggest that aspalathin is absorbed and metabolised in mice to mostly sulphate conjugates detected in urine. Mechanistically, we showed that aspalathin is not actively transported by the glucose transporters, but presumably passes the monolayer paracellularly.

Aspalathin from Rooibos (Aspalathus linearis): A Bioactive C-glucosyl Dihydrochalcone with Potential to Target the Metabolic Syndrome

“…Notably, Huang et al [11] found that aspalathin absorption increased when present in green rooibos extract as opposed to the pure compound, indicating that other plant components present in the extract may assist in its transport across the membrane. In contrast, Bowles et al [10] found absorption of pure aspalathin to be similar to that when present in green rooibos extract. Experimental differences may account for this disparity in results, in particular the substantially higher aspalathin concentration, as well as the higher permeability of the monolayer used by Huang et al [11].…”

“…3) and thus also the whole dried shoots (4-10 %) [20]. Rooibos produced in the tradi- [7,8] Molecular weight 452.412 [7,8] Melting point 152-154°C [9] Polar surface area (Å 2 ) 208 [7] Log P (predicted) 2.07 [8] Log D (pH 7.4) (experimental) 0.13 [10] Log D (pH 5.5) (experimental) − 0.347 [11] H bond acceptors 11 [7,8] H bond donors 9 [7,8] Freely rotating bonds 6 [7,8] "Rule of 5′′ violations 2 [8] Solubility at pH 2 (µM) 153 [10] Solubility at pH 6.5 (µM) 123 [10] Solubility in FaSSIF at pH 6.5 (µM) 119 [10] ▶ Fig. 1 Commercial plantation of cultivated A. linearis (rooibos).…”

“…5 B). For a study on the permeability of aspalathin in a Caco-2 cell model [10], the stability of aspalathin as a pure compound and when present in an aspalathin-rich green rooibos extract was determined under cell culture conditions (pH 7.4) over 2 h in HBSS (▶ Fig. 5 C).…”

“…5 Effect of pH on stability of pure aspalathin (ASP) and when present in green rooibos extract. Conditions were as follows: A citric acidphosphate buffer at room temperature (adapted from De Beer et al [30]); B phosphate buffered saline at room temperature (AA = 1 % ascorbic acid) (unpublished data; HPLC analysis as described in Joubert et al [48]); C HBSS under cell culture conditions (37°C, 5 % CO 2 , 95 % humidity) (unpublished data; HPLC analysis as described in Bowles et al [10]).…”

Skeletal Muscle as a Therapeutic Target for Natural Products to Reverse Metabolic Syndrome

“…While Stalmach et al [26], using high-performance liquid chromatography-mass spectrometry method, showed that O-methyl-aspalathin-O-glucuronide and eriodictyol-O-sulfate were the main metabolites excreted following ingestion of rooibos extract containing 10-fold higher levels of aspalathin in human subjects. In addition, a recent study by Bowles et al [27] showed that aspalathin can be absorbed and metabolized to mostly sulfate conjugates detected in the urine of mice. However, additional evidence is required to establish the pharmacokinetic profile of aspalathin.…”