Background: Human serum albumin acts as a carrier protein to a variety of drugs and
aids their transport. Andrographis paniculata, a herbal plant has been used as a source of traditional
medicine in the Asian countries. Among the various constituents of this plant, andrographolide is
the most active and is being used from centuries in the treatment of many chronic and infectious
Objective: The present study was designed to evaluate the interaction and binding affinity of andrographolide
with HSA, by molecular docking, chromatographic and spectral studies.
Methods: Andrographolide was docked with crystal structure of human serum albumin (1AO6)
using Auto Dock Vina software and the interactions were analyzed by a visualizing software py-
MOL. For further characterization and confirmation, andrographolide (3x10-5 M) and HSA (0.001,
0.005, 0.01, 0.02, 0.04 M) sample mixtures were incubated at 37°C for 3h in a metabolic shaker,
followed by centrifugation. The supernatant and the filtrate were analyzed by UV spectroscopy,
HPLC, CD and FTIR spectral analysis.
Results: The docking studies revealed that andrographolide interacted with HSA and formed hydrogen
bonds with Trp 214, Arg 218 and Lys 444 amino acid residues. The UV spectral analysis
revealed a decrease in the absorption peak of HSA due to its interaction with andrographolide. A
new peak was observed at retention time 7.45 min by HPLC analysis and the Bmax was found to be
7.5 ± 0.4 mg protein with a Kd value of 1.89 mM, indicating interaction of andrographolide with
HSA. The CD spectra results suggested, a marginal decrease in the negative ellipticity without any
significant shift in peak, indicating the stabilization of the HSA-andrographolide complex. The
FTIR analysis of the andrographolide-HSA mixture showed a peak at wave number 1637 cm−1 (a
shift of amide I groups from 1646 cm−1) and 1016 cm−1 which corresponded to the ligand, confirming
the complex formation.
Conclusion: The molecular docking studies demonstrated the interactions of andrographolide to the
crystal structure of HSA. The chromatographic and spectroscopic analysis confirmed the binding of
andrographolide with HSA and their complex formation. Overall the present studies conclude the
binding of andrographolide to HSA protein, favoring its pharmacokinetics.