The effect of asparagus laricinus fractions on major drug metabolising enzymes – cyp3a4 and 2d6

Abstract

Asparagus laricinus Burch. is a shrub widely used in traditional South African medicine and is known to contain diverse phytochemicals such as flavonoids, phenolics, saponins, alkaloids and terpenoids that may interact with drug-metabolising enzymes. Because nearly 50% and 25% of drugs used in clinical practice are metabolised by CYP3A4 and CYP2D6 respectively – with CYP3A4 being the predominant hepatic form and CYP2D6 showing genetic polymorphism – herbal constituents that inhibit these enzymes may cause clinically significant herb-drug interactions by altering the plasma concentration of concomitant medications. Although the pharmacological activity of A. laricinus has been documented, its possible effect on CYP3A4 and CYP2D6 activity had not previously been studied. The aim of this study was to analyse the phytochemical composition of Asparagus laricinus leaves, evaluate their effects on the major drug-metabolising enzymes CYP3A4 and CYP2D6, and to investigate the kinetic profile of these enzymes in the presence of the plant fractions. The crude methanolic leaf extract was fractionated into seven parts (A–I), and qualitative phytochemical screening was performed on each. Phenolic glycosides, flavonoid conjugation and steroidal saponins were identified as possible contributors, tentatively confirmed by LC-MS. Using in-vitro fluorescent-based high-throughput assays, a very strong dose-dependent inhibition of the enzymes was observed. Fraction H showed the highest dual activity (CYP3A4 IC₅₀ = 0.0026 μM; CYP2D6 IC₅₀ = 1.5 μM) in a mixed/non-competitive interaction, while fractions C and E were selective inhibitors of CYP2D6 and CYP3A4, respectively. The kinetic profiling supported the presence of potent inhibitory compounds within these fractions. Using in vitro, fluorescent-based, high-throughput assays, a very strong dose-dependent inhibition of the enzymes was observed. Fraction H showed the highest dual %inhibition effect (CYP3A4 % inhibition = 95,84%; CYP2D6 % inhibition = 91.26%) in a mixed/non-competitive interaction, while Fractions C and E were selective inhibitors of CYP2D6 and CYP3A4, respectively. The kinetic profiling supported the presence of potent inhibitory compounds within these fractions. Overall, the findings indicate that some A. laricinus fractions contain strong CYP3A4 and CYP2D6 inhibitors, suggesting a potential risk of herb-drug interactions when the plant is used concurrently with medications metabolised by these enzymes. This highlights the importance of pharmacovigilance, particularly in cancer patients who use A. laricinus preparations alongside traditional medicines.