Guowen Li

Development of a myricetin/hydroxypropyl-β-cyclodextrin inclusion complex: Preparation, characterization, and evaluation

Myricetin shows low oral bioavailability (<10%) in rats due to poor aqueous solubility, though it has various pharmacological activities. Complexation with cyclodextrins (CDs) is a potent pharmaceutical method to enhance the bioavailability of poorly soluble compounds. The myricetin/HP-β-CD inclusion complex was prepared and confirmed by DSC, PXRD, and SEM. Here, the inclusion mode is described in detail with regard to structural and energetic aspects using a phase solubility diagram and 1H NMR, NOESY, and FT-IR spectra. The water solubility and dissolution rate of myricetin were greatly enhanced by forming the myricetin/HP-β-CD inclusion complex. Consequently, the oral bioavailability of the myricetin/HP-β-CD inclusion complex in rats was effectively increased 9.4-fold over free myricetin, and its antioxidant activity was also improved. The present study provides useful information for the potential application of complexation with myricetin, a naturally occurring hydrophobic phenolic compound in herbal medicine.

A Novel Strategy for Pharmaceutical Cocrystal Generation Without Knowledge of Stoichiometric Ratio: Myricetin Cocrystals and a Ternary Phase Diagram

PurposeTo develop a streamlined strategy for pharmaceutical cocrystal preparation without knowledge of the stoichiometric ratio by preparing and characterizing the cocrystals of myricetin (MYR) with four cocrystal coformers (CCF).MethodsAn approach based on the phase solubility diagram (PSD) was used for MYR cocrystals preparation and the solid-state properties were characterized by differential scanning calorimetry (DSC), fourier transform-infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). The ternary phase diagram (TPD) was constructed by combining the PSD and nuclear magnetic resonance (NMR) data. After that, the TPD was verified by traditional methods. The dissolution of MYR in the four cocrystals and pure MYR within three different media were also evaluated.ResultsA simple research method for MYR cocrystal preparation was obtained as follows: first, the PSD of MYR and CCF was constructed and analyzed; second, by transforming the curve in the PSD to a TPD, a region of pure cocrystals formation was exhibited, and then MYR cocrystals were prepared and identified by DSC, FT-IR, PXRD, and SEM; third, with the composition of the prepared cocrystal from NMR, the TPD of the MYR-CCF-Solvent system was constructed. The powder dissolution data showed that the solubility and dissolution rate of MYR was significantly enhanced by the cocrystals.ConclusionsA novel strategy for pharmaceutical cocrystals preparation without knowledge of the stoichiometric ratio based on the TPD was established and MYR cocrystals were successfully prepared. The present study provides a systematic approach for pharmaceutical cocrystal generation, which benefits the development and application of cocrystal technology in drug delivery.

Effects of stabilizing agents on the development of myricetin nanosuspension and its characterization: An in vitro and in vivo evaluation

Although myricetin has various pharmacological applications, it shows low oral bioavailability (<10%) in rats due to its poor aqueous solubility. To overcome this issue, myricetin nanosuspensions were developed and the effects of stabilizers were investigated. Based on the particle size and zeta potential, stabilizers soya lecithin, TPGS, HP-β-CD, and/or a combination thereof were used. The prepared nanosuspensions were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray powder diffraction (XRD). The resulting myricetin nanosuspensions contained particles in the size range of 300-500 nm and were physically stable. Myricetin was partially transformed from crystalline to amorphous forms in the presence of different excipients after the nanosizing process. The solubility and in vitro dissolution of all myricetin nanosuspensions were greatly increased compared with those of the myricetin powder. Consequently, the relative bioavailability in rats were 2.44, 3.57, 1.61, and 2.96 for nanosuspensions stabilized with TPGS, soya lecithin, soya lecithin+TPGS, and HP-β-CD+TPGS, respectively, relative to that of the coarse myricetin. This research demonstrated that nanosuspension is a promising strategy for delivering poor water-soluble drugs such as myricetin and that stabilizers played a critical role in the formulation design of myricetin nanosuspensions.

Effects of solid dispersion and self-emulsifying formulations on the solubility, dissolution, permeability and pharmacokinetics of isorhamnetin, quercetin and kaempferol in total flavones of Hippophae rhamnoides L.

The aim of this study was to investigate the effects of solid dispersions (SD) and self-emulsifying (SE) formulations on the solubility and absorption properties of active components in total flavones of Hippophae rhamnoides L. (TFH). The solubility, dissolution rate, permeability and pharmacokinetics of isorhamnetin, quercetin and kaempferol in TFH SD/SE formulations and TFH were compared. The results showed that the solubility and dissolution rate of isorhamnetin, quercetin and kaempferol in SD/SE formulations were significantly enhanced compared to those in TFH, however, their intestinal permeability was comparable. The bioavailability of isorhamnetin, quercetin and kaempferol in rats remarkably increased after oral administration of TFH SD formulations compared to TFH, but there was no significant increase after oral administration of TFH SE formulations. The results of this study indicated the SD formulations on the improvement of pharmacokinetic properties of isorhamnetin, quercetin and kaempferol in TFH were much better than those of SE formulations. The improvement of pharmacokinetic properties of isorhamnetin, quercetin and kaempferol in TFH by SD formulations was probably ascribed to the enhancement of the solubility and dissolution of the three components, but was not relevant to the intestinal permeability. Therefore, as for herb extracts containing multiple components, especially for their major components with poor water solubility, solid dispersion formulations might have the better potential to enhance their bioavailability.

Transport characteristics of isorhamnetin across intestinal Caco-2 cell monolayers and the effects of transporters on it.

Flavonoid isorhamnetin occurs in various plants and herbs, and demonstrates various biological effects in humans. This work will clarify the isorhamnetin absorption mechanism using the Caco-2 monolayer cell model. The isorhamnetin transport characteristics at different concentrations, pHs, temperatures, tight junctions and potential transporters were systemically investigated. Isorhamnetin was poorly absorbed by both passive diffusion and active transport mechanisms. Both trans- and paracellular pathways were involved during isorhamnetin transport. Active transport under an ATP-dependent transport mechanism was mediated by the organic anion transporting peptide (OATP); isorhamnetins permeability from the apical to the basolateral side significantly decreased after estrone-3-sulfate was added (p<0.01). Efflux transporters, P-glycoproteins (P-gp), breast cancer resistance proteins (BCRP) and multidrug resistance proteins (MRPs) participated in the isorhamnetin transport process. Among them, the MRPs (especially MRP2) were the main efflux transporters for isorhamnetin; transport from the apical to the basolateral side increased 10.8-fold after adding an MRP inhibitor (MK571). This study details isorhamnetins cellular transport and elaborates isorhamnetins absorption mechanisms to provide a foundation for further studies.

Phytic acid enhances the oral absorption of isorhamnetin, quercetin, and kaempferol in total flavones of Hippophae rhamnoides L.

AIM Total flavones of Hippophae rhamnoides L. (TFH) have a clinical use in the treatment of cardiac disease. The pharmacological effects of TFH are attributed to its major flavonoid components, isorhamnetin, kaempferol, and quercetin. However, poor oral bioavailability of these flavonoids limits the clinical applications of TFH. This study explores phytic acid (IP6) enhancement of the oral absorption in rats of isorhamnetin, kaempferol, and quercetin in TFH. METHODS In vitro Caco-2 cell experiments and in vivo pharmacokinetic studies were performed to investigate the effects of IP6. The aqueous solubility and lipophilicity of isorhamnetin, quercetin, and kaempferol were determined with and without IP6, and mucosal epithelial damage resulting from IP6 addition was evaluated by MTT assays and morphology observations. RESULTS The Papp of isorhamnetin, kaempferol, and quercetin was improved 2.03-, 1.69-, and 2.11-fold in the presence of 333 μg/mL of IP6, respectively. Water solubility was increased 22.75-, 15.15-, and 12.86-fold for isorhamnetin, kaempferol, and quercetin, respectively, in the presence of 20mg/mL IP6. The lipophilicity of the three flavonoids was slightly decreased, but their hydrophilicity was increased after the addition of IP6 in the water phase as the logP values of isorhamnetin, kaempferol, and quercetin decreased from 2.38±0.12 to 1.64±0.02, from 2.57±0.20 to 2.01±0.04, and from 2.39±0.12 to 1.15±0.01, respectively. The absorption enhancement ratios were 3.21 for isorhamnetin, 2.98 for kaempferol, and 1.64 for quercetin with co-administration of IP6 (200 mg/kg) in rats. In addition, IP6 (200 mg/kg, oral) caused neither significant irritation to the rat intestines nor cytotoxicity (400 μg/mL) in Caco-2 cells. CONCLUSIONS The oral bioavailability of isorhamnetin, kaempferol, and quercetin in TFH was enhanced by the co-administration of IP6. The main mechanisms are related to their enhanced aqueous solubility and permeability in the presence of IP6. In summary, IP6 is a potential absorption enhancer for pharmaceutical formulations that is both effective and safe.

Preparation and evaluation of chitosan-based nanogels/gels for oral delivery of myricetin.

A novel nanogel/gel based on chitosan (CS) for the oral delivery of myricetin (Myr) was developed and evaluated comprehensively. The particle size of the obtained Myr-loaded CS/β-glycerol phosphate (β-GP) nanogels was in the range of 100-300nm. The rheological tests showed that the sol-gel transition happened when the nanogels were exposed to physiological temperatures, and 3D network structures of the gelatinized nanogels (gels) were confirmed by Scanning Electron Microscopy. Myr was released from CS/β-GP nanogel/gel in acidic buffers via a Fickian mechanism, and this release was simultaneously accompanied by swelling and erosion. Moreover, the nanogel/gel exhibited no cytotoxicity by MTT assay, and the oral bioavailability of Myr in rats was improved with an accelerated absorption rate after Myr was loaded into CS/β-GP nanogel/gel. In summary, all of the above showed that CS/β-GP nanogel/gel was an excellent system for orally delivering Myr.

Development of a pharmaceutical cocrystal with solution crystallization technology: Preparation, characterization, and evaluation of myricetin-proline cocrystals.

Myricetin shows low oral bioavailability (<10%) in rats due to poor aqueous solubility, although it has demonstrated various pharmacological activities such as those related to anticancer, anti-diabetes, and hepatic protection. To overcome this issue, in this study, pharmaceutical cocrystals were designed to efficiently deliver myricetin by oral administration. A 1:2 stoichiometric cocrystal of myricetin with proline was prepared successfully by solution crystallization based on the ternary phase diagram (TPD) principle, and it is presented as a new sphericity-like crystalline phase characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). The formation of myricetin-proline cocrystals was a spontaneous and exothermic process, probably due to the supramolecular interactions between themselves, which were determined by Fourier transform-infrared spectroscopy (FT-IR). Consequently, the dissolution efficiency of myricetin from cocrystals was increased 7.69-fold compared with that of coarse myricetin, and the oral bioavailability of myricetin cocrystals in rats was enhanced by approximately 3.03 times compared with that of pure myricetin. The present study provides useful information for the potential application of cocrystal technology for water-insoluble drugs, especially flavonoid compounds.

Comparison of isorhamnetin absorption properties in total flavones of Hippophae rhamnoides L. with its pure form in a Caco-2 cell model mediated by multidrug resistance-associated protein.

Total flavones of Hippophae rhamnoides L. (TFH) are extracted from the widely distributed thorny bush Sea buckthorn (Hippophae rhamnoides L.). Isorhamnetin (IS) is one of the representative ingredients in TFH. In this study, the absorption properties of IS in TFH and its pure form were compared through transepithelial transport and cellular uptake experiments in a Caco-2 cell model. Our results show that the absorption properties of IS in TFH and its pure form were remarkably different: (1) Both PappAB and PappBA of IS in TFH were dramatically increased compared with those of IS pure form; consequently, its Pratio was 2.3-fold higher than that of IS; (2) Both the accumulation and efflux of IS in TFH were significantly enhanced compared with the single compound. One likely reason for these differences is that the multiple components in TFH significantly down regulated the mRNA expression level of MRP2, which lead to a decrease in the protein level of MRP2, based on western blotting and RT-PCR assays. This study highlights the significant differences in the absorption properties of flavonoid components in different forms and the potential multi-component interactions in TFH.

Assessment of intestinal absorption of total flavones of Hippophae rhamnoides L. in rat using in situ absorption models

Purpose: The objective of this study was to investigate the absorption behavior of total flavones of Hippophae rhamnoides L. (TFH) (the sum of isorhamnetin and quercetin as the index component) in the rat intestine using in situ circulation method. Methods: The accumulated TFH absorption and related absorption parameters were calculated. Furthermore, the influences of Cremophor ELP and the P-glycoprotein inhibitor, verapamil, on the intestinal absorption of TFH were studied using the in situ circulation model. Results and Discussion: The results showed that the absorption of TFH increased linearly with its concentration, indicating that a passive diffusion process was dominated. There were no significant differences in the absorption of TFH in three small intestine segments of duodenum, jejunum, and ileum and at different concentrations of Cremophor ELP ranging from 0.25% to 1% (P > 0.05). With the presence of P-gp inhibitor, verapamil, in the circulation fluid, the accumulated absorption of TFH did not increase significantly (P > 0.05). Further studies on the solubility and permeability enhancement of TFH should be investigated to develop new TFH products with high bioavailability.