Unraveling the binding mechanism of asiatic acid with human serum albumin and its biological implications

Abstract

Asiatic acid (AsA), a naturally occurring pentacyclictriterpenoid found in Centella asiatica, plays a major role in neuroprotection, anticancer, antioxidant, and hepatoprotective activities. Human serum albumin (HSA), a blood plasma protein, participates in the regulation of plasma osmotic pressure and transports endogenous and exogenous substances. The study undertaken to analyze the drug-binding mechanisms of HSA is crucial in understanding the bioavailability of drugs. In this study, we analyzed the cytotoxic activity of AsA on HepG2 (human hepatocellular carcinoma) cell lines and its binding, conformational, docking, molecular simulation studies with HSA under physiological pH 7.2. These studies revealed a clear decrease in the viability of HepG2 cells upon exposure to AsA in a dose-dependent manner with an IC50 of 45 μM. Further studies showed the quenching of intrinsic fluorescence of HSA by AsA with a binding constant of KAsA = 3.86 ± 0.01 × 10(4) M(-1), which corresponds to the free energy of (ΔG) -6.3 kcal M(-1) at 25 °C. Circular dichroism (CD) studies revealed that there is a clear decrease in the α-helical content from 57.50 ± 2.4 to 50% ± 2.3 and an increase in the β-turns from 25 ± 0.65 to 29% ± 0.91 and random coils from 17.5% ± 0.95 to 21% ± 1.2, suggesting partial unfolding of HSA. Autodock studies revealed that the AsA is bound to the subdomain IIA with hydrophobic and hydrophilic interactions. From molecular dynamics, simulation data (RMSD, Rg and RMSF) emphasized the local conformational changes and rigidity of the residues of both HSA and HSA-AsA complexes.

Elucidating the binding interaction of andrographolide with the plasma proteins: biophysical and computational approach

“…Similar results were observed, with a decreased a-helical content and an increased b-sheet and random coil content, in earlier reports from our laboratory. [11][12][13]29,[55][56][57] It is clearly evident that there was only a marginal decrease in the negative ellipticity in the region of far-UV CD, without any signicant shi in peaks. The similarity between the CD spectral shapes of free HSA and HSA-ANDR suggested that the structure of HSA was also predominantly a-helix ( Table 2), indicating that the binding of the drug to HSA induced a slight decrease in the ahelical structure content of the protein, with a minor increase in the b-sheets and random coils.…”

Pharmacological Properties, Molecular Mechanisms, and Pharmaceutical Development of Asiatic Acid: A Pentacyclic Triterpenoid of Therapeutic Promise

“…The available preclinical and clinical pharmacokinetic data suggest that AA is bioavailable in almost every tissue. It's distributed to many components of the body by binding with albumin (Gokara et al, 2014 ). Following intravenous injection, asiaticoside gets widely distributed in several organs and is metabolized extensively and recovered as AA in the feces (Hengjumrut et al, 2018 ).…”

Studies on the interaction between promethazine and human serum albumin in the presence of flavonoids by spectroscopic and molecular modeling techniques

“…It has been reported that the content of α-helix in the secondary structure of HSA is 67% [51]. The differences in α-helical contents could be originated to the different structural arrangements of the protein in the solid state (X-ray structure) and in aqueous solution (CD measurements) [71,72].…”