Enhancement of Dissolving Capacity and Reducing Gastric Mucosa Irritation by Complex Formation of Resibufogenin with β-Cyclodextrin or 2-Hydroxypropyl-β-cyclodextrin

Abstract

Resibufogenin (RBG) is a natural medicinal ingredient with promising cardiac protection and antitumor activity. However, poor solubility and severe gastric mucosa irritation restrict its application in the pharmaceutical field. In this study, the inclusion complex of RBG with β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) was prepared using the co-evaporation method, and the molar ratio of RBG to CD was determined to be approximately 1:2 by continuous variation plot for both CDs. The formation of inclusion complexes between RBG and each CD (RBG/β-CD and RBG/HP-β-CD) was evaluated by phase solubility study, Fourier transform infrared spectroscopy, and thin-layer chromatography. Powder X-ray diffraction and differential scanning calorimetry confirmed drug amorphization and encapsulation in the molecular cage for both CDs. Moreover, the inclusion complexes' morphologies were observed using scanning electron microscopy. The dissolution rate of the inclusion complexes was markedly improved compared to that of RBG, and the complexes retained their antitumor activity, as shown in the in vitro cytotoxicity assay on a human lung adenocarcinoma cancer (A549) cell line. Moreover, less gastric mucosal irritation was observed for the inclusion complex. Thus, the inclusion complex should be considered a promising strategy for the delivery of poorly water-soluble anticancer agents, such as RBG.

Keywords: cyclodextrin; dissolution rate; gastric mucosa irritation; inclusion complex; resibufogenin.

Figure 1

The chemical structures of resibufogenin (RBG).

Figure 2

Phase solubility diagrams of RBG/β-CD and RBG/HP-β-CD system. The CD concentration was in the range of 0–15 mM.

Figure 3

Possible inclusion mode of the inclusion complexes.

Figure 4

(A) FT-IR spectra, (B) PXRD patterns and (C) DSC curves of (a) RBG, (b) β-CD, (c) RBG/β-CD PM (1:2 molar ratio), (d) RBG/β-CD complex, (e) HP-β-CD, (f) RBG/HP-β-CD PM (1:2 molar ratio), and (g) RBG/HP-β-CD complex.

Figure 5

SEM of (a) RBG, (b) β-CD, (c) HP-β-CD, (d) RBG/β-CD complex, and (e) RBG/HP-β-CD complex.

Figure 6

TLC analysis of RBG/β-CD (a) and RBG/HP-β-CD (b) inclusion complex (1—reference solution; 2—ethanol extract; 3—ethyl acetate extract).

Figure 7

Dissolution profiles of RBG, RBG/β-CD PMs, RBG/β-CD inclusion complexes (A), RBG/HP-β-CD PMs, and RBG/HP-β-CD inclusion complexes (B) in PBS (pH 6.8) at 37 °C.

Figure 8

Pathological section of stomach (×10) after oral administration of (A) CMC-Na, (B) acetylsalicylic acid, (C) RBG intact, (D) RBG/β-CD, and (E) RBG/HP-β-CD.