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    ABSTRACT: This study reports the use of para-sulphonato calix[8]arene to produce stable complexes with improved bioavailability for nifedipine, a calcium-channel blocker that is practically insoluble in water. Thermal analysis and electrospray ionisation mass spectroscopy confirmed that nifedipine formed complexes with the calixarenes in a size dependent way. The most stable, soluble complexes was formed with para-sulphonato calix[8]arene. Complexation was weakest with the calix[4]arene while complexation with the calix[6]arene was intermediate. However, the calix[4 and 6]arenes changed the chemical stability of the drug in solution because significant amounts of the nitroso-pyridine derivative was produced, proposing an interaction between the nifedipine bearing a H substituent at the N-1 position and the calixarenes. This oxidative degradation of the drug was greatest when combined with the calix[6]arene. Simultaneous oral ingestion of the calix[6 or 8]arenes significantly increased the bioavailability of the drug after oral administration in male Sprague-Dawley rats while not influencing CYP3A activities in the liver. The pharmacokinetic parameters of the nifedipine: para-sulfonato calix[8]arene complexes showed it was bioequivalent to a nifedipine PEG-solution. The absolute bioavailability for both formulations was ca. 60 %.
    Current Drug Discovery Technologies 07/2008; 5(2):129-39.
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    Li Yang, Wenzhan Yang, Dianzhou Bi, Qun Zeng
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    ABSTRACT: A novel modified film-hydration-dilution method was employed to prepare highly encapsulated interferon-alpha-2b containing liposomes for intramuscular sustained release. The liposomes produced by this technique were a mixture of mainly unilamellar vesicles and a small number of multilamellar vesicles. The trapping efficiency was above 80%. With at least 60-fold dilution, Triton X-100 at the concentration of 0.3% (w/v) in phosphate buffered saline (PBS) was able to solubilize phospholipids without denaturing the protein and/or interfering with the enzyme-linked immunoassay (ELISA). After three homogenization cycles under a pressure of 70 MPa the size of liposomes was reduced from 978 to 101 nm while the activity of interferon-alpha-2b decreased by 9.9% compared to the control. Although liposomes were physically stable for 22 months at 4 degrees C the mean size of the liposomes increased slightly from 101 to 122 nm. The levels of free interferon-alpha-2b at the site of intramuscular injection decreased rapidly with only 4.15% of initial dose retained at the injection site after 0.33 h following injection of an interferon-alpha-2b solution (nonencapsulated). In contrast, interferon-alpha-2b encapsulated in liposomes was retained at the site of intramuscular injection at higher levels than free interferon-alpha-2b (p < 0.05). Larger liposomes containing interferon-alpha-2b (978 nm) were the most effective for local retention because 27.8% of interferon-alpha-2b was retained after 24 h. These liposomes have the potential to be topically injected for treating genital herpes with prolonged interferon levels at the local injection site. Since the smaller liposomes (75.8 and 101 nm) retained interferon-alpha-2b at the injection site for shorter times while enhancing the blood circulation of the drug, they are potentially good carriers for systemic therapy with higher bioavailability and liver targeting.
    European Journal of Pharmaceutics and Biopharmaceutics 09/2006; 64(1):9-15. · 3.83 Impact Factor
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    ABSTRACT: In this study, the thermal behavior of three hydrated water-soluble 4-sulphonato calix[n]arenes was investigated. The melting points, heats of fusion, and heats of solution of the calix[4]arene, calix[6]arene and calix[8]arene were 277, 262, and 270°C; 192, 242 and 351 kJ/mol; and 30, 58 and 63 kJ/mol, respectively. Lower heat of fusion, smaller increase in entropy and smaller heat of solution of the calix[4]arene compared to the calix[6]arene and calix[8]arene showed that less heat was required to break up the crystal lattice of the smaller macromolecule. This apparent anomaly is rationalized in terms of smaller cooperativity of interaction between the molecules of calix[4]arene in the crystal lattice, although the strength of the individual interactions is stronger as evidenced by the higher melting point. TGA analysis indicated that about 17–20% of water was associated with the calix[n]arenes. Both TGA and hot stage microscopy results indicated that upon heating these molecules underwent stepwise water loss. TGA kinetics showed that the 4-sulphonato-calix[8]arene lost water easier than the other two calixarenes. The moisture adsorption behavior of all calixarenes followed type II isotherms. For the same amount of material, the calix[6]arene adsorbed more moisture than the calix[4]arene and the calix[8]arene. Moreover, dehydrated less crystalline 4-sulphonic-calix[n]arenes powders are hydroscopic.
    Supramolecular Chemistry 09/2005; 17(6):485-496. · 1.55 Impact Factor
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    Wenzhan Yang, Melgardt M de Villiers
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    ABSTRACT: The present study investigated the effect of water-soluble 4-sulphonato-calix[n]arenes, cyclodextrins, and combinations of these macromolecules on the aqueous solubility of a poorly water-soluble drug, niclosamide. Complexation between the macromolecules and niclosamide was confirmed by thermal analysis and phase solubility studies in a pH 7.0 Mcllvaine buffer kept at 30 degrees C. Results show that the increase in solubility ranked as follows: 4-sulphonato-calix[6]arene + hydroxypropyl-beta-cyclodextrin (HP-beta-CD) > 4-sulphonato-calix[6]arene + beta-cyclodextrin > 4-sulphonato-calix[6]arene + gamma-cyclodextrin = HP-beta-CD > 4-sulphonato-calix[6]arene > 4-sulphonato-calix[8]arene = 4-sulphonato-calix[4]arene > beta-cyclodextrin . Type B phase solubility profiles were observed, indicating a decrease in solubility at concentrations > 0.004 to 0.005 mol/L of the 4-sulphonato-calix[n]arenes or combinations of 4-sulphonato-calix[6]arene and the cyclodextrins. However, below this concentration, the greatest increase in the aqueous solubility niclosamide was observed when 4-sulphonato-calix[6]arene and HP-beta-CD were combined. This increase in solubility was additive.
    The AAPS Journal 02/2005; 7(1):E241-8. · 4.39 Impact Factor
  • Wenzhan Yang, Melgardt M de Villiers
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    ABSTRACT: In this study, the solubilizing effect of 4-sulphonic calix[n]arenes on the poorly water soluble drug nifedipine was investigated. 4-Sulphonic calix[n]arenes are water-soluble phenolic cyclooligomers that form complexes with neutral molecules such as nifedipine. Solubility experiments were performed at 30 degrees C using the Higuchi rotating bottle method. The amount of nifedipine in solution was determined by HPLC. The results showed that the size of the 4-sulphonic calix[n]arenes, the pH of solubility medium, and the concentration of the calix[n]arenes all significantly changed the solubility of nifedipine. 4-Sulphonic calix[8]arene improved the solubility of nifedipine the most, about 3 times the control at 0.008 M and pH 5, followed by 4-sulphonic calix[4]arene, about 1.5 times the control at 0.008 M and pH 5, while in the presence of 4-sulphonic calix[6]arene, the solubility of nifedipine was decreased. The possible mechanisms involving in the complexation between 4-sulphonic calix[4]arenes, 4-sulphonic calix[8]arene and nifedipine may be a combination of hydrogen bonding, hydrophobic bonding, and possibly electron donor-acceptor interactions. However, the degree to which these forces promote the formation of nifedipine:4-sulphonic calix[n]arene complexes with increased solubility was limited by conformational changes in the 4-sulphonic calix[n]arene molecules.
    European Journal of Pharmaceutics and Biopharmaceutics 12/2004; 58(3):629-36. · 3.83 Impact Factor
  • Wenzhan Yang, Melgardt M de Villiers
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    ABSTRACT: The solubilization of the practically water insoluble drug furosemide by guest:host inclusion complexation with 4-sulphonic calix[n]arenes has been reported. The 4-sulphonic calix[n]arenes are water-soluble phenolic cyclooligomers that form inclusion complexes with neutral molecules. The solubility of furosemide in acidic (pH < 4) aqueous solutions containing increasing concentrations of the calixarenes was determined at 30 degrees C and the concentration of furosemide in solution was determined by HPLC. Results showed that the molecular size of the 4-sulphonic calix[n]arenes and the concentration of the calix[n]arenes significantly influenced the increase in the solubility of furosemide. 4-Sulphonic calix[6]arene improved the solubility of furosemide the most (+/-104%) followed by 4-sulphonic calix[8]arene (+/-84-102%), while 4-sulphonic calix[4]arene increased the solubility of furosemide the least (+/-73-81%). The increase in furosemide solubility afforded by the calixarenes was most probably the result of the incorporation of the non-polar portions of the furosemide molecule into the non-polar cavities of the calixarenes similar to furosemide:cyclodextrin complexes. The driving force for this interaction was the reduction in the non-polar-water interfacial surface area when the furosemide (guest) molecules were inserted into the 4-sulphonic calix[n]arenes (host).
    Journal of Pharmacy and Pharmacology 06/2004; 56(6):703-8. · 2.03 Impact Factor
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    ABSTRACT: Triclosan, an antimicrobial, although widely incorporated into many skin care products, toothpastes, and liquid soaps, presents formulation difficulties because it is practically insoluble in water. The objective of this study was to improve the aqueous solubility of triclosan through solubilization, complexation, and salt formation. The solubility of triclosan in distilled water and in phosphate buffers (pH 7.4) was determined at 30 degrees C. The order of solubilizing performance of the solubilizers was: N-methylglucamine> or =L-arginine>sodium lauryl sulfate>beta-cyclodextrin> or =hydroxypropyl-beta-cyclodextrin>ethanolamine>sodium benzoate>sodium methyl 4-hydroxybenzoate>triethanolamine> or =diethanolamine. These solubilizers increased the solubility of triclosan from 80- to 6000-fold. Micellar solubilization and the formation of either salts or complexes are postulated as possible mechanisms for the increase in the solubility of triclosan by the surfactant sodium lauryl sulphate, the cyclic sugar derivatives beta-cyclodextrin and 2-hydropropyl-beta-cyclodextrin, the amino acid L-arginine, and the amino sugar alcohol N-methylglucamine. Furthermore, although the bacteriostatic efficacy of triclosan was significantly increased when solubilized with N-methylglucamine, L-arginine, and ethanolamine, increased solubilization did not increase the effectiveness of triclosan for all solubilizers tested.
    Journal of cosmetic science 54(6):537-50. · 0.28 Impact Factor
  • Wenzhan. Yang
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    ABSTRACT: Copyright by the author. Vita. Thesis (Ph.D.) -- University of Louisiana at Monroe, 2005. Bibliography: leaves 244-256.

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