Enhanced Antioxidant and Neuroprotective Properties of Pterostilbene (Resveratrol Derivative) in Amorphous Solid Dispersions

Abstract

In this study, amorphous solid dispersions (ASDs) of pterostilbene (PTR) with polyvinylpyrrolidone polymers (PVP K30 and VA64) were prepared through milling, affirming the amorphous dispersion of PTR via X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC). Subsequent analysis of DSC thermograms, augmented using mathematical equations such as the Gordon-Taylor and Couchman-Karasz equations, facilitated the determination of predicted values for glass transition (T_g), PTR's miscibility with PVP, and the strength of PTR's interaction with the polymers. Fourier-transform infrared (FTIR) analysis validated interactions maintaining PTR's amorphous state and identified involved functional groups, namely, the 4'-OH and/or -CH groups of PTR and the C=O group of PVP. The study culminated in evaluating the impact of amorphization on water solubility, the release profile in pH 6.8, and in vitro permeability (PAMPA-GIT and BBB methods). In addition, it was determined how improving water solubility affects the increase in antioxidant (ABTS, DPPH, CUPRAC, and FRAP assays) and neuroprotective (inhibition of cholinesterases: AChE and BChE) properties. The apparent solubility of the pure PTR was ~4.0 µg·mL^-1 and showed no activity in the considered assays. For obtained ASDs (PTR-PVP30/PTR-PVPVA64, respectively) improvements in apparent solubility (410.8 and 383.2 µg·mL^-1), release profile, permeability, antioxidant properties (ABTS: IC₅₀ = 52.37/52.99 μg·mL^-1, DPPH: IC₅₀ = 163.43/173.96 μg·mL^-1, CUPRAC: IC_0.5 = 122.27/129.59 μg·mL^-1, FRAP: IC_0.5 = 95.69/98.57 μg·mL^-1), and neuroprotective effects (AChE: 39.1%/36.2%, BChE: 76.9%/73.2%) were confirmed.

Keywords: Couchman–Karasz equation; Gordon–Taylor equation; amorphous solid dispersion; antioxidation; glass transition; miscibility; molecular modeling; neuroprotection; polyvinylpyrrolidone; pterostilbene.

Figure 1

XRPD analysis, range 5–40° 2Θ: (a) pterostilbene (PTR, black line), PVP K30 (red line), pterostilbene-PVP30 physical mixture (PTR-PVP30 (ph.m.), blue line), pterostilbene-PVP30 amorphous solid dispersion (PTR-PVP30 (ASD), green line); (b) pterostilbene (PTR, black line), PVP VA64 (red line), pterostilbene-PVPVA64 physical mixture (PTR-PVPVA64 (ph.m.), blue line), pterostilbene-PVPVA64 amorphous solid dispersion (PTR-PVPVA64 (ASD), green line).

Figure 2

Thermal analysis: TG thermogram of pterostilbene (black line), TG thermogram of PVP K30 (red line), TG thermogram of PVP VA64 (blue line), DSC thermogram of pterostilbene (black dashed line, first heating).

Figure 3

DSC analysis, second heating: (a) amorphous pterostilbene (black line), PVP K30 (red line), PTR-PVP30 amorphous solid dispersion (PTR-PVP30 (ASD), green line); (b) amorphous pterostilbene (black line), PVP VA64 (red line), PTR-PVPVA64 amorphous solid dispersion (PTR-PVPVA64 (ASD), green line).

Figure 4

Structure of (a) pterostilbene; (b) PVP K30; (c) PVP VA64. Legend: rings A and B—two phenolic rings of pterostilbene.

Figure 5

FTIR-ATR analysis, range 400–1800 cm ⁻¹: (a) pterostilbene (black line), PVP K30 (red line), pterostilbene-PVP30 physical mixture (PTR-PVP30 (ph.m.), blue line), pterostilbene-PVP30 amorphous solid dispersion (PTR-PVP30 (ASD), green line); (b) pterostilbene (black line), PVP VA64 (red line), pterostilbene-PVPVA64 physical mixture (PTR-PVPVA64 (ph.m.), blue line), pterostilbene-PVP VA64 amorphous solid dispersion (PTR-PVPVA64 (ASD), green line). Red-colored numbers correspond to the PVP bands in ASDs.

Figure 6

The released profiles of pterostilbene (PTR) and PTR-PVP amorphous solid dispersions (PTR-PVP30 and PVP-VA64) at pH 6.8.

Figure 7

Proposed binding mode of pterostilbene (PTR) with human acetylcholinesterase (AChE, PDB id: 4BDT). The key interactions of PTR with residues in the active sites of AChE. Legend: ASP—aspartic acid, TRP—tryptophan, TYR—tyrosine, grey dashed line—hydrophobic interaction, blue solid line—hydrogen bond, green dashed line—π-stacking.

Figure 8

Proposed binding mode of pterostilbene (PTR) with human butyrylcholinesterase (BChE, PDB id: 4BDS). The key interactions of PTR with residues in the active sites of BChE. Legend: ASN—asparagine, ASP—aspartic acid, GLY—glycine, ILE—isoleucine, TRP—tryptophan, grey dashed line—hydrophobic interaction, blue solid line—hydrogen bond.