Enzymes and Enzyme Inhibitors in Drug Research

Alzheimer’s disease (AD) and diabetes are non-communicable diseases with global impacts. Inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are suitable therapies for AD, while α-amylase and α-glucosidase inhibitors are employed as antidiabetic agents. Compounds were isolated from the medicinal plant Terminalia macroptera and evaluated for their AChE, BChE, α-amylase, and α-glucosidase inhibitions. From ¹H and ¹³C NMR data, the compounds were identified as 3,3′-di-O-methyl ellagic acid (1), 3,3′,4′-tri-O-methyl ellagic acid-4-O-β-D-xylopyranoside (2), 3,3′,4′-tri-O-methyl ellagic acid-4-O-β-D-glucopyranoside (3), 3,3′-di-O-methyl ellagic acid-4-O-β-D-glucopyranoside (4), myricetin-3-O-rhamnoside (5), shikimic acid (6), arjungenin (7), terminolic acid (8), 24-deoxysericoside (9), arjunglucoside I (10), and chebuloside II (11). The derivatives of ellagic acid (1–4) showed moderate to good inhibition of cholinesterases, with the most potent being 3,3′-di-O-methyl ellagic acid, with IC₅₀ values of 46.77 ± 0.90 µg/mL and 50.48 ± 1.10 µg/mL against AChE and BChE, respectively. The compounds exhibited potential inhibition of α-amylase and α-glucosidase, especially the phenolic compounds (1–5). Myricetin-3-O-rhamnoside had the highest α-amylase inhibition with an IC₅₀ value of 65.17 ± 0.43 µg/mL compared to acarbose with an IC₅₀ value of 32.25 ± 0.36 µg/mL. Two compounds, 3,3′-di-O-methyl ellagic acid (IC₅₀ = 74.18 ± 0.29 µg/mL) and myricetin-3-O-rhamnoside (IC₅₀ = 69.02 ± 0.65 µg/mL), were more active than the standard acarbose (IC₅₀ = 87.70 ± 0.68 µg/mL) in the α-glucosidase assay. For α-glucosidase and α-amylase, the molecular docking results for 1–11 reveal that these compounds may fit well into the binding sites of the target enzymes, establishing stable complexes with negative binding energies in the range of −4.03 to −10.20 kcalmol⁻¹. Though not all the compounds showed binding affinities with cholinesterases, some had negative binding energies, indicating that the inhibition was thermodynamically favorable. Full article

The β-adrenergic drug Mirabegron, a drug initially used for the treatment of an overactive bladder, has new potential indications and is hydrolyzed by butyrylcholinesterase (BChE). This compound is one of the only arylacylamide substrates to be catabolized by BChE. A steady-state kinetic analysis at 25 °C and pH 7.0 showed that the enzyme behavior is Michaelian with this substrate and displays a long pre-steady-state phase characterized by a burst. The induction time, τ, increased with substrate concentration (τ ≈ 18 min at maximum velocity). The kinetic behavior was interpreted in terms of hysteretic behavior, resulting from a slow equilibrium between two enzyme active forms, E and E′. The pre-steady-state phase with the highest activity corresponds to action of the E form, and the steady state corresponds to action of the E′ form. The catalytic parameters were determined as k_cat = 7.3 min⁻¹ and K_m = 23.5 μM for the initial (burst) form E, and k_cat = 1.6 min⁻¹ and K_m = 3.9 μM for the final form E′. Thus, the higher affinity of E′ for Mirabegron triggers the slow enzyme state equilibrium toward a slow steady state. Despite the complexity of the reaction mechanism of Mirabegron with BChE, slow BChE-catalyzed degradation of Mirabegron in blood should have no impact on the pharmacological activities of this drug. Full article