Novel liposome-based multicomponent systems for the protection of photolabile agents

Preparation of DRV Liposomes

Dried reconstituted vesicle (DRV) liposomes are formulated under mild conditions. The method has the capability to entrap substantially higher amounts of hydrophilic solutes, compared to other passive-loading liposome preparation methods. These characteristics make this liposome type ideal for entrapment of labile substances, such as peptides, proteins, or DNA's (or other nucleotides or oligonucleotides), or in general biopharmaceuticals and sensitive drugs. In this chapter, all possible types of DRV liposomes (in respect to the encapsulated molecule characteristics and/or their applications in therapeutics) are introduced, and preparation methodologies (for each type) are described in detail.

Molecular recognition and photoprotection of riboflavin in water by a biomimetic host

A water-soluble tetralactam macrocycle with 2,6-diethoxynaphthalene groups as side walls is able to strongly bind riboflavin (K_a >10⁷ M^-1) in water through hydrogen bonding and the hydrophobic effect. The encapsulated riboflavin can be stabilized by the host against photo-degradation under UV-vis irradiation, which may be harnessed to extend the shelf life of riboflavin.

Light-sensitive drugs in topical formulations: stability indicating methods and photostabilization strategies

Photostability tests applied on commercial specialties for topical use have demonstrated a greater vulnerability of several drugs, due to greater exposure to light than other pharmaceutical forms. Photodegradation of a drug can considerably modify its pharmacokinetic behavior by varying the therapeutic index. The evaluation of the degradation profile of a drug, according to the ICH rules, is of primary importance in developing an appropriate topical formulation. Advanced strategies have been proposed to increase the protection from the light of the photolabile drugs. Supramolecular systems have been investigated to improve both pharmacokinetic profile and photostability. In this review, the more recent stability-monitoring methods for the analysis of drugs in topical formulations are collected and the main approaches for the drug photostabilization are discussed.

Preparation of DRV Liposomes

Dried reconstituted vesicles (DRV) are liposomes that are formulated under mild conditions and have the capability to entrap substantially high amounts of hydrophilic solutes (compared to other types of liposomes). These characteristics make this liposome type ideal for entrapment of labile substances, as peptide, protein, or DNA vaccines, or in general biopharmaceuticals and sensitive drugs. In this chapter, all possible types of DRV liposomes (with respect to the encapsulated molecule characteristics and/or their applications in therapeutics) are introduced, and preparation methodologies (for each type) are described in detail.

Interaction between the photosensitizer lumichrome and human serum albumin: effect of excipients

Lumichrome (Lc) is a photodegradation product of riboflavin that can be used as a photosensitizer (PS) in antibacterial photodynamic therapy (aPDT). The binding of Lc with plasma proteins such as human serum albumin (HSA) could affect its efficiency as PS. Excipients are necessary to prepare stable formulations to be used in aPDT and they may affect the PS-HSA binding. Hydroxypropyl (HP)-α, β, γ-cyclodextrin (CD), polyethylene glycol 400 (PEG400) and Pluronic^® F-127 (PF127) were selected as model excipients in this study. The intrinsic HSA fluorescence quenching and absorption and fluorescence spectroscopy were used to evaluate the Lc-HSA interaction in the absence and presence of excipients. Nano-differential scanning calorimetry (DSC) was used to determine the effect of excipients on HSA. The photostability of the samples was also evaluated. The combined results showed a modest interaction between Lc and HSA which was reduced mainly by HPβCD. No major alterations of the HSA nano-DSC thermogram were observed after addition of excipients. HSA did enhance Lc photodegradation. The presence of PF127 did also induce photochemical destabilization of Lc independent of HSA. In conclusion, HPαCD, HPγCD and PEG400 seemed to be the excipients more suitable for use in topical preparations containing Lc.

Formulation and stabilization of norfloxacin in liposomal preparations

A number of liposomal preparations of norfloxacin (NF) containing variable concentrations of phosphatidylcholine (PC) (10.8-16.2mM) have been formulated and an entrapment of NF to the extent of 41.7-56.2% was achieved. The values of apparent first-order rate constants (kobs) for the photodegradation of NF in liposomes (pH7.4) lie in the range of 1.05-2.40×10(-3)min(-1) compared to a value of 8.13×10(-3)min(-1) for the photodegradation of NF in aqueous solution (pH7.4). The values of kobs are a linear function of PC concentration indicating an interaction of PC and NF during the reaction. The second-order rate constant for the photochemical interaction of PC and NF has been determined as 8.92×10(-2)M(-1)min(-1). Fluorescence measurements on NF in liposomes indicate a decrease in fluorescence with an increase in PC concentration as a result of formation of NF(-) species which exhibits poor fluorescence. Dynamic light scattering has shown an increase in the size of NF encapsulated liposomes with an increase in PC concentration. The stabilization of NF in liposomes is achieved by the formation of a charge-transfer complex between NF and PC.

Characterization and evaluation of synthetic riluzole with β-cyclodextrin and 2,6-di-O-methyl-β-cyclodextrin inclusion complexes

β-Cyclodextrin (β-CD) and 2,6-di-O-methyl-β-cyclodextrin (DM-β-CD) inclusion complexes with riluzole (RLZ) were prepared to improve water solubility and broaden potential pharmaceutical applications. CDs/RLZ inclusion complexes were confirmed via phase solubility studies, FT-IR spectroscopy, PXRD, DSC, (1)H NMR, and SEM. Phase solubility studies indicated that β-CD and DM-β-CD can form 1:1 inclusion complexes with RLZ, and the stability constants were 663.17 and 1609.07M(-1), respectively. Water solubility and dissolution rate of RLZ were significantly improved in complex forms, implying that the inclusion complexes may develop pharmaceutical applications. Preliminary in vitro cytotoxicity assay also showed that RLZ hepatotoxicity was not increased in the inclusion complexes.

Spectral and electrochemical study of host-guest inclusion complex between 2,4-dinitrophenol and β-cyclodextrin

The formation of host-guest inclusion complex of 2,4-dinitrophenol (2,4-DNP) with nano-hydrophobic cavity of β-cyclodextrin (β-CD) in solution phase was studied by UV-visible spectrophotometer and electrochemical method (cyclic voltammetry, CV). The prototropic behaviors of 2,4-DNP with and without β-CD and the ground state acidity constant (pK(a)) of host-guest inclusion complex (2,4-DNP-β-CD) were studied. The binding constant of inclusion complex at 303K was calculated using Benesi-Hildebrand plot and thermodynamic parameter (ΔG) was also calculated. The solid inclusion complex formation between β-CD and 2,4-DNP was confirmed by (1)H NMR, FT-IR, XRD and SEM analysis. A schematic representation of this inclusion process is proposed by molecular docking studies using PatchDock server.

Preparation of DRV liposomes

Dried reconstituted vesicles (DRV) are liposomes that are formulated under mild conditions and have the capability to entrap substantially high amounts of hydrophilic solutes (compared with other types of liposomes). These characteristics make this liposome type ideal for entrapment of labile substances, as peptide, protein or DNA vaccines and sensitive drugs. In this chapter, we initially introduce all possible types of DRV liposomes (in respect to the encapsulated molecule characteristics and/or their applications in therapeutics) and discuss in detail the preparation methodologies for each type.

Preparation, Characterization and Pharmacokinetics of Liposomes-Encapsulated Cyclodextrins Inclusion Complexes for Hydrophobic Drugs

Liposomes-encapsulated indomethacin/cyclodextrins (IMC/ CD) inclusion complexes were prepared. The characteristics and pharmacokinetics of the combined system were investigated. The high drug entrapment values of 2.38 +/- 0.16 microg/mg and 2.48 +/- 0.12 microg/mg for liposomes-encapsulated IMC/ beta-CD and IMC/HP-beta-CD inclusion complexes were achieved, as only 1.60 +/- 0.09 microg/mg for conventional liposomes. Encapsulating IMC/CD inclusion complexes into liposomes resulted in a slow release of drug. Following intravenous administration, both liposomes-encapsulated inclusion complexes showed significantly improved AUC(0 - infinity) compared with that of conventional liposomes (p < 0.05). After intramuscular administration, C(max) has been increased to 5.21 +/- 1.14 microg x ml(-1) and 6.02 +/- 1.22 microg x ml(- 1) for liposomes-encapsulated IMC/ beta -CD and IMC/HP-beta -CD inclusion complexes, respectively, whereas only 2.43 +/- 0.69 microg x ml(- 1) for liposomes-encapsulated free drug (p < 0.01).

Effect of preparation technique on the properties of liposomes encapsulating ketoprofen–cyclodextrin complexes aimed for transdermal delivery

The combined approach of cyclodextrin complexation and entrapment in liposomes was investigated in order to develop an effective topical formulation of ketoprofen. Equimolar complex of drug and hydroxypropyl-beta-cyclodextrin (HPbetaCyd) was added at different concentrations to the aqueous phase of liposomes consisting of phosphatidylcholine and cholesterol (60%/40%, w/w). Liposomes were prepared with different techniques, such as thin layer evaporation, freezing and thawing, extrusion through microporous membrane, and reverse phase evaporation method, obtaining, respectively, multi-lamellar vesicles (MLV), frozen and thawed MLV (FATMLV), small uni-lamellar vesicles (SUV) and large uni-lamellar vesicles (LUV). Size and morphology of the different types of liposomes were investigated by light scattering analysis, transmission electron microscopy, and confocal laser scanning microscopy, whereas drug entrapment efficiency was determined by dialysis experiments. Cyclodextrin complexation improved drug solubilization and allowed a strong improvement of its entrapment into the aqueous liposomal phase. Liposome preparation method and operating conditions clearly affected both liposome size and drug loading capacity. Encapsulation efficiency increased with increasing the complex concentration up to 10 mM, and was in the order MLV>LUV>SUV. An opposite behaviour was observed for FATMLV, probably due to the freezing phase required by such a preparation method, which reduced the complex solubility. Moreover, it was not possible to use higher complex concentrations, due to the destabilizing effect of cyclodextrins toward the liposomal membrane. Permeability studies of drug-HPbetaCyd complexes, directly in solution or incorporated in liposomes, performed across artificial membranes simulating the skin behaviour, highlighted, as expected, a prolonged release effect of liposomal formulations. Furthermore, the drug permeation rate depended on the vesicle characteristics and varied in the order: SUV>MLV=FATMLV>LUV. Therefore, the most suitable liposome preparation method can be suitably selected on the basis of drug encapsulation efficiency and/or desired drug release rate.

Cyclodextrins in drug delivery: an updated review

The purpose of this review is to discuss and summarize some of the interesting findings and applications of cyclodextrins (CDs) and their derivatives in different areas of drug delivery, particularly in protein and peptide drug delivery and gene delivery. The article highlights important CD applications in the design of various novel delivery systems like liposomes, microspheres, microcapsules, and nanoparticles. In addition to their well-known effects on drug solubility and dissolution, bioavailability, safety, and stability, their use as excipients in drug formulation are also discussed in this article. The article also focuses on various factors influencing inclusion complex formation because an understanding of the same is necessary for proper handling of these versatile materials. Some important considerations in selecting CDs in drug formulation such as their commercial availability, regulatory status, and patent status are also summarized. CDs, because of their continuing ability to find several novel applications in drug delivery, are expected to solve many problems associated with the delivery of different novel drugs through different delivery routes.

Preparation and characterisation of liposomes encapsulating ketoprofen–cyclodextrin complexes for transdermal drug delivery

Multilamellar vesicle (MLV) liposomes containing ketoprofen-cyclodextrin complexes intended for drug topical delivery were prepared, with the aim of simultaneously exploiting the favourable properties of both carriers. Drug complexes with beta-cyclodextrin (betaCyd) and hydroxypropyl-betaCyd (HPbetaCyd), prepared by coevaporation and sealed-heating methods, were characterised by differential scanning calorimetry, hot stage microscopy, scanning electron microscopy and tested for dissolution properties. The coevaporated system with HPbetaCyd was the most effective, enabling an about 11-fold increase in drug dissolution. Drug and drug-Cyd systems were incorporated in MLV liposomes prepared by the thin layer evaporation technique. All liposomal formulations were characterised for encapsulation efficiency, particle size and morphology, using dialysis, light scattering and transmission electron microscopy techniques, respectively. MLV formation was negatively influenced by the presence of Cyd; nevertheless, it was possible to prepare stable MLVs containing ketoprofen-Cyd complexes. The presence of the Cyd complex affected MLV dimensions but not their lamellar structure. The complex with HPbetaCyd, in virtue of its greater stability than the betaCyd one, allowed higher percentages of encapsulation and gave rise to more stable MLV systems. Permeability studies of drug and drug-Cyd complexes, as such or incorporated in liposomes, performed both across artificial membranes and rat skin, highlighted a favourable effect of Cyd on drug permeation rate, due to its solubilizing action; by contrast, unexpectedly, no skin-permeation enhancer property of liposomes has been evidenced. Confocal laser scanning microscopy studies carried out with the rhodamine-Cyd complex as fluorescent marker, confirmed such results, showing that the label permeated deeper across rat skin layers when it was in solution than when entrapped in liposomes.

Photolysis of riboflavin in aqueous solution: a kinetic study

The kinetics of photolysis of aqueous riboflavin solutions on UV and visible irradiation has been studied in the pH range 1-12 using a specific multicomponent spectrophotometric method for the simultaneous determination of riboflavin and its major photoproducts (formylmethylflavin, lumichrome and lumiflavin). The apparent first-order rate constants for the photodegradation reactions in the pH range have been determined. The log k-pH profiles indicate that riboflavin has maximum photostability around pH 5-6, at which the rate of oxidation-reduction of the molecule is lowest. The cationic and anionic forms of riboflavin are non-fluorescent and less susceptible to photolysis than the non-ionised molecule as indicated by the relatively slow rates below pH 3.0 and above pH 10.0. The rate of photolysis is increased up to 80-fold at pH 10.0, compared to that at pH 5.0, due to increase in redox potentials with an increase in pH and consequently the ease with which the molecule is oxidised. The increase in rate at pH 3.0, compared to that at pH 5.0, appears to be due to the involvement of the excited singlet state as well as the triplet state in riboflavin degradation. The apparent first-order rate constants for the photolysis of riboflavin at pH 5.0-10.0 with UV and visible radiation are 0.185 x 10(-2) to 13.182 x 10(-2)min(-1) and 0.098 x 10(-2) to 7.762 x 10(-2)min(-1), respectively.

Design and monitoring of photostability systems for amlodipine dosage forms

Photostability of amlodipine (AML) has been monitored in several pharmaceutical inclusion systems characterized by plurimolecular aggregation of the drug and excipients with high molecular weight. Several formulations including cyclodextrins, liposomes and microspheres have been prepared and characterized. The photodegradation process has been monitored according to the conditions suggested by the ICH Guideline for photostability testing, by using a light cabinet equipped with a Xenon lamp and monitored by spectrophotometry. The formulations herein tested have been found to be able to considerably increase drug stability, when compared with usual pharmaceutical forms. The residual concentration detected in the inclusion complexes with cyclodextrins and liposomes was 90 and 77%, respectively, while a very good value of 97% was found for microspheres, after a radiant exposure of 11,340 kJm(-2).

Interfacial interactions between amphiphilic cyclodextrins and physiologically relevant cations

The compression isotherms of a series of amphiphilic cyclodextrins, formed (a) by acylation at the secondary hydroxyl face and (b) by acylation accompanied by varying degrees of sulfatation (DS) at the primary hydroxyl face (DS=0, 4, and 7), have been studied on subphases of pure water and of water containing NaCl, KCl, MgCl(2), and CaCl(2) at inter- and extracellular concentrations. The formation of solid lipid nanoparticles (SLNs) by two of the molecules has been observed, while these do not aggregate at concentrations of monovalent salts up to 150 mM for the sulfated derivative. In the presence of divalent salts one of these with a DS=0 for sulfatation degree flocculates at divalent salt concentrations below 0.1 mM while the other with a DS=4 flocculates at Mg(2+) concentration above 5 mM and a Ca(2+) concentration above 3 mM. AFM noncontact mode imaging has been carried out, in air, for the SLNs deposited on mica.

A Plackett-Burnam screening design directs the efficient formulation of multicomponent DRV liposomes

A computer-based technique was applied for the optimization of recently described multicomponent protective liposomal formulations. These formulations contain riboflavin in either free form or complexed with gamma-cyclodextrin as a model drug, sensitive to photochemical degradation, as well as various light absorbers and antioxidants incorporated into the lipid bilayer and/or the aqueous phase of liposomes. During the liposomal preparation, a series of 11 factors were isolated as important to affect their effectiveness as stabilization systems. These factors were related, first, to the composition of liposomes and, second, to variations during the preparation procedure. The Plackett--Burnam design described in this study was applied for the isolation of the significant factors in order to concentrate more on them. The stabilization ratio of the vitamin was the response variable of the system to be optimized. In order to assure the presence of the examined components in liposomes, the entrapment values were calculated for all the materials, either spectrophotometrically or using second-order derivative spectrophotometry. The optimum formulation should be characterized from the higher protection of the drug.

Formulation and stability testing of photolabile drugs

Exposure of a drug to irradiation can influence the stability of the formulation, leading to changes in the physicochemical properties of the product. The influence of excipients of frequently used stabilizers is often difficult to predict and, therefore, stability testing of the final preparation is important. The selection of a protective packaging must be based on knowledge about the wavelength causing the instability. Details on drug photoreactivity will also be helpful in order to minimize side-effects and/or optimize drug targeting by developing photoresponsive drug delivery systems. This review focuses on practical problems related to formulation and stability testing of photolabile drugs.

Drug/cyclodextrin/hydroxy acid multicomponent systems. Properties and pharmaceutical applications

The objective of this mini-review is to summarize the findings concerning the properties and the pharmaceutical applications of multicomponent complexes made of a sparingly water-soluble amino-type drug, a cyclodextrin, and a hydroxy carboxylic acid. Simultaneous complexation and salt formation with these acids significantly increase the solubilizing power, allowing us to reduce the amount of cyclodextrin necessary for making the targeted formulation. In many cases, the aqueous solubility of the hydrophobic drug can be enhanced by several orders of magnitude, while that of CD can be enhanced more than 10-fold. The mechanism through which these complexes elicit their synergetic effects on the drug solubility is also discussed. Finally, some general observations are made concerning the structural requirements of the drug necessary for exploiting the aforementioned effect.

A computer-based expert system designs and analyzes a 2(k - p) fractional factorial design for the formulation optimization of novel multicomponent liposomes

A computer-based technique based on a 2(k - p) fractional factorial design was applied for the optimization of recently described multicomponent protective liposomal formulations. These formulations contain sodium ascorbate (vitamin C) as a model drug sensitive to photochemical oxidation, as well as oil red O and/or oxybenzone as oil soluble light absorbers, incorporated into the lipid bilayers and sulisobenzone as a water soluble light absorber incorporated into the aqueous phase of liposomes. The three light absorbers (present or absent) incorporated in multilamellar liposomes and the drug in free or in complexed with alpha-cyclodextrin form comprised the four factors of the system. The stabilization ratio and the percentage entrapment in the liposomes of the vitamin were the two response variables of the system to be optimized. The entrapment values were calculated for all the materials either spectrophotometrically or by using second order derivative spectrophotometry. The response variables were predicted by multiple regression equations comprising combinations of the four formulation factors. Both the higher entrapment and the higher protection for the drug should characterize the optimum formulation.