Structural insights into the inclusion complexes between clomiphene citrate and β-cyclodextrin: The mechanism of preferential isomeric selection

Development and evaluation of novel krill oil-based clomiphene microemulsion as a therapeutic strategy for PCOS treatment

Polycystic ovary syndrome (PCOS) is frequently diagnosed hormonal disorder with reproductive and metabolic complications. The most common symptoms include cyst in ovaries, anovulation, insulin resistance, and obesity. Clomiphene citrate, an ovulating agent, is the first-line drug used to treat PCOS. We hypothesized that clomiphene citrate, by stimulating ovarian function, with krill oil used as an oil phase to improve solubility, by addressing PCOS-associated symptoms might be effective in PCOS. Hence, our goal was to target hormonal imbalance along with PCOS-associated symptoms using a single formulation. The concentration of water (X1), oil (X2), and Smix (surfactant-cosurfactant mixture) (X3) were selected as independent variables, in a simplex lattice design, from microemulsion area derived from a pseuodoternary phase diagram while the globule size (Y1) was selected as a dependent parameter. The optimized microemulsion showed good sphericity having 41 nm globule size, 0.32 poly dispersibility index and + 31 mV zeta potential. The optimized microemulsion was further evaluated in-vivo using letrozole-induced PCOS rats. Formulation treated group reversed the effect of letrozole on body weight and estrus cycle in comparison to the disease control group (p < 0.001). The formulation was also effective in reducing insulin resistance, cholesterol and serum testosterone level (p < 0.001). The in vivo results were supported by histopathological studies where the formulation-treated group showed a marked decrease in the number of cystic follicles and a remarkable increase in the number of growing follicles at variable stages, similar to the normal control group. Thus, the results confirmed that novel krill oil-based clomiphene microemulsion may become a promising therapeutic choice for the treatment of PCOS.

Molecular recognition of flunarizine dihydrochloride and β-cyclodextrin inclusion complex by NMR and computational approaches

Background

Flunarizine dihydrochloride (FLN) is used in the prophylactic treatment of migraine, vertigo, occlusive peripheral vascular disease and epilepsy. Cyclodextrins (CDs) are chiral, truncated cone shaped macrocycles known for their inner hydrophobic and outer hydrophilic site. They form complexes with hydrophobic drug molecules and enhance the solubility and bioavailability of such compounds by enhancing drug permeability through mucosal tissues. NMR spectroscopy and computational docking have been recognized as an important tool for the interaction study of CDs-drug inclusion complexes in solution state.

Results

The structural assignments of FLN and β-CD protons were determined by ¹H NMR and 2D ¹H-¹H COSY NMR spectroscopy. ¹H NMR spectroscopic studies of FLN, β-CD and their mixtures confirmed the formation of β-CD-FLN inclusion complex in solution. ¹H NMR titration data for β-CD-FLN inclusion complex showed 1:1 stoichiometry, an association constant of K_a = 157 M⁻¹ and change in Gibbs free energy of ∆G = − 12.65 kJ mol⁻¹. The binding constant of the β-CD inclusion complex with two nearly similar structures, FLN and cetirizine dihydrochloride, were compared. Two-dimensional ¹H-¹H ROESY spectral data and molecular docking studies showed the modes of penetration of the aromatic rings from the wider rim side into the β-CD cavity. The possible geometrical structures of the β-CD-FLN inclusion complex have been proposed in which aromatic rings protrude close to the narrower rim of the β-CD truncated cone.

Conclusion

NMR spectroscopic studies of FLN, β-CD and FLN:β-CD mixtures confirmed the formation of 1:1 inclusion complex in solution at room temperature. Two-dimensional ¹H-¹H ROESY together with molecular docking study confirmed that the F-substituted aromatic ring of FLN penetrates into β-CD truncated cone and the tail of aromatic rings were proximal to narrower rim of β-CD. The splitting of aromatic signals of FLN in the presence of β-CD suggests chiral differentiation of the guest FLN by β-CD.

Electronic supplementary material

The online version of this article (10.1186/s13065-018-0395-4) contains supplementary material, which is available to authorized users.