Influence of formulation on photoinactivation of bacteria by lumichrome.

Lumichrome, a photodegradation product of riboflavin, is an endogenous compound in humans. The compound is more photostable and a more efficient photogenerator of singlet oxygen than riboflavin. It absorbs radiation in the UVA and blue-light region, which can be an advantage in antibacterial photodynamic therapy (aPDT) of superficial infections. The aim of this study was to investigate the in vitro aPDT effect of various lumichrome pharmaceutical formulations. Solutions of lumichrome (10(-5) - 10(-3)M) were prepared in plain phosphate buffered saline (PBS) or in PBS solutions containing cyclodextrins, DMSO, PEG 400 or polyoxamers (Pluronic). Supersaturated solutions of lumichrome in PBS were prepared via the cosolvent and solvent evaporation method. Phototoxic effects of selected lumichrome preparations were studied in planktonic Gram-positive (E. faecalis) and Gram-negative (E. coli) bacteria models. The UVA/blue light source emitted mainly in the range 340-440 nm. Lumichrome was up to tenfold more phototoxic against Gram-positive than to Gram-negative bacteria. Bacterial eradication was induced after exposure of lumichrome formulations (PBS, PEG 400 and HPγCD) combined with 24J/cm2 UVA/blue light. Increasing the concentration of lumichrome did not enhance the phototoxic effect, probably due to radiation attenuation in the highly absorbing solution (inner filter effect). Cyclodextrins were efficient enhancers of the lumichrome solubility in aqueous solutions, but inhibited the phototoxic effect. The study demonstrates that assuming the use of an optimized formulation, lumichrome has potential as a UVA/blue light photosensitizer in aPDT.

Influence of crystal modification on the photoinduced color change in riboflavin.

Two different qualities of riboflavin (RF) i.e., synthetic (RFs) and biosynthetic riboflavin (RFbs) have been investigated with respect to photoinduced color change in the solid state. Several methods (XRD, FT-IR, VIS-, NIR- and fluorescence spectroscopy) were employed to elucidate the properties of the crystalline structure of RFs and RFbs and the influence of irradiation on the color and structural changes of the samples in the solid state. It was shown that RFs an RFbs represent two different crystal modifications of riboflavin and that RFbs can easily be transformed into a dihydrate upon exposure to humidity. Based on the observed irreversible color change and reduction in fluorescence intensity upon irradiation, an irreversible photoreduction of the molecule was assumed in case of RFs. A more pronounced, reversible color change and reversible reduction in fluorescence intensity indicated a reversible photoreduction process in the case of RFbs. The mechanism of these processes was further investigated by means of NIR and FT-IR spectrophotometry. It is apparent from the current study that the crystal modification of RF can strongly influence the solid state photochemistry of this molecule.

Influence of vehicle properties and excipients on hydrolytic and photochemical stability of curcumin in preparations containing Pluronics: studies of curcumin and curcuminoids XLVIII.

The influence of vehicle properties and excipients on the hydrolytic and photochemical stability of curcumin in Pluronic preparations, and the interactions between curcumin and Pluronics was investigated. Curcumin was found to be degraded by general acid-base catalyzed hydrolytic degradation in alkaline preparations. The degradation rate of curcumin was higher in carbonate buffer than in phosphate buffer (pH 8.8), while it was higher in phosphate buffer than in citrate buffer (pH 7.8). At pH 8.0-8.8 the degradation rate of curcumin increased compared to preparations with pH <8.0. The stabilizing effect of the Pluronics against hydrolytic degradation of curcumin was only detectable at pH 8.0-8.8, and it was highest for F127 and lowest for P85, in phosphate buffer pH 8.8. An increase in the ionic strength increased the stabilization against hydrolytic degradation of curcumin by all Pluronics. Addition of ethanol decreased the hydrolytic stability of curcumin in all Pluronics. Addition of PEG 400 decreased the hydrolytic stability in preparation with either P123 or F127 while the degradation in preparations with P85 remained the same as in P85 preparations without PEG 400. Vehicle properties and excipients did not to any large degree influence the spectroscopic properties or the photostability of curcumin in Pluronic preparations. Photochemical half life of curcumin was in the minutes range. Spectrophotometric data indicate that Pluronic aggregates most likely solubilize curcumin through hydrophobic interactions, although hydrogen-bonding may also be involved.

Influence of aqueous media properties on aggregation and solubility of four structurally related meso-porphyrin photosensitizers evaluated by spectrophotometric measurements.

Porphyrin photosensitizers tend to aggregate in aqueous solutions even in the micromolar concentration range. This is a challenge during formulation of e.g., parenteral preparations for photodynamic cancer therapy, or preparations for local or topical administration in antimicrobial photodynamic therapy. Monomerization is essential to achieve biocompatible drug formulations of high bioavailability and physiological response (i.e., photoreactivity) and low toxicity. The aggregation and solubilization of four structurally related meso-tetraphenyl porphyrin photosensitizers with nonionic (4-hydroxy), anionic (4-sulphonate; 4-carboxy) and cationic (4-trimethylanilinium) substituents were evaluated in various vehicles by use of UV-Vis spectroscopy. Substituents, overall charge and charge distribution influenced the pKa-values and interaction of the porphyrins with different solvents, excipients and impurities. Modification of medium polarity and solubilization by the nonionic surfactant Tween 80 adjusted the acid-base equilibria and increased the solubility by reduction of porphyrin aggregation. The selected porphyrins were sensitive towards ionic strength, temperature and inorganic impurities to various extents. The results will be further used during development of parenteral and topical formulations of porphyrin photosensitizers for use in photodynamic therapy of cancer and bacterial infections.

Solid dispersions for preparation of phototoxic supersaturated solutions for antimicrobial photodynamic therapy (aPDT): Studies on curcumin and curcuminoides L.

Curcumin is under investigation as a potential photosensitizer (PS) in antimicrobial photodynamic therapy (aPDT). The therapeutic potential of curcumin as a PS is limited by its low aqueous solubility, susceptibility to hydrolytic and photolytic degradation, and limited phototoxicity toward Gram negative (G-) bacteria. Supersaturated solutions of curcumin have demonstrated high phototoxicity toward several species of Gram positive (G+) bacteria as well as the G-Escherichia (E) coli. Thus, solid dispersions that can form supersaturated solutions of curcumin upon hydration may be beneficial in aPDT. In the present study, solid dispersions of curcumin have been prepared through lyophilization of concentrated solutions obtained from dissolution of hydroxypropyl-ß-cyclodextrin (HPßCD)-curcumin co-precipitates. Hydroxypropyl methylcellulose (HPMC) was added to curcumin solutions prior to lyophilization. The resulting lyophilizates were porous, amorphous and hydrated and dissolved rapidly in contact with a model physiological salt solution. The detected drug load of the lyophilizates was in the range 0.5-1.0% (w/w) and was dependent on the selected ratio between HPßCD and curcumin in the co-precipitate. The lyophilizate with the highest drug load could easily be dissolved in aqueous medium to form curcumin solutions of relevant concentrations for aPDT (i.e., 10µM). Selected solutions of the curcumin solid dispersions showed a pronounced decrease in curcumin concentration up to 90% after storage for 168h, which indicated that supersaturated curcumin solutions were initially formed upon dissolution of the lyophilizates. Both freshly prepared and 2days old solutions of one selected curcumin lyophilizate induced significant inactivation of E. coli (∼1% bacterial survival) after exposure to a light dose of only 5J/cm(2).

Solubilization of the photosensitizers TPCS(2a) and TPPS(2a) in aqueous media evaluated by time-resolved fluorescence analysis.

The pH-dependent aggregation of the novel photosensitizer TPCS(2a) is investigated at low concentration (c = 10(-6) M) in aqueous media by means of time-correlated single-photon counting, and compared to that of the chemically related photosensitizer TPPS(2a). The efficacy of selected solubilizers, i.e., various nonionic Pluronic block copolymers and the nonionic surfactant Tween 80, in inhibiting aggregation of the two photosensitizers is evaluated, which is important for the further formulation of TPCS(2a).

Photoinactivation of Staphylococcus epidermidis biofilms and suspensions by the hydrophobic photosensitizer curcumin--effect of selected nanocarrier: studies on curcumin and curcuminoides XLVII.

Solubilization and stabilization from rapid degradation by the use of nanocarriers are necessary to exploit curcumin's phototoxic potential towards pathogenic bacteria. However, maintenance of the phototoxicity requires a careful selection of type and amount of nanocarrier. The phototoxicity of an aqueous supersaturated curcumin solution without nanocarrier was compared to that of curcumin solubilized in polyethylene glycol 400 (PEG 400), Pluronic® F 127 (F 127) and hydroxypropyl-γ-cyclodextrin (HPγCD) on Staphylococcus (S.) epidermidis biofilms and suspensions. The nanocarriers stabilized the hydrophobic photosensitizer (PS) towards physical precipitation and hydrolytic degradation; however, photobleaching was pronounced (46-100% degradation) after irradiation with a dose of ≈ 9 J/cm(2) blue light depending on selected nanocarrier. Complete inactivation of S. epidermidis in suspension was achieved after exposure of ≈ 5 J/cm(2) combined with curcumin in 20% PEG 400 and 0.5% HPγCD and less than 1J/cm(2) light in case of a supersaturated curcumin solution. Curcumin in 1.5% F 127 induced phototoxicity towards bacterial biofilms; however, it was not phototoxic towards planktonic S. epidermidis. All curcumin preparations investigated demonstrated significant and similar phototoxicity towards biofilms (13-29% bacterial survival). A ≈ 9 J/cm(2) light dose was not sufficient to eradicate S. epidermidis biofilm completely under the current conditions.

Influence of cosolvents, ionic strength and the method of sample preparation on the solubilization of curcumin by Pluronics and HP-gamma-cyclodextrin. Studies of curcumin and curcuminoids, XLIV.

Curcumin was solubilized by Pluronics and the concentration of dissolved curcumin seemed to be related to the number of propylene oxide units in the Pluronic polymer. All Pluronics showed a maximum solubilizing capacity at a certain curcumin: Pluronic molar ratio and exceeding this molar ratio resulted in precipitation of curcumin when following the samples for 356 hours. PEG 400 could to a certain extent stabilize the supersaturated samples, while ethanol physically destabilized the samples. Ionic strength did not influence the solubilization of curcumin by the Pluronics. Supersaturation and precipitation inhibition caused a higher concentration of curcumin in samples prepared by SEM compared to samples prepared by SFM (i.e. the thermodynamic solubility).

Studies on curcumin and curcuminoids. XLVI. Photophysical properties of dimethoxycurcumin and bis-dehydroxycurcumin.

The steady-state absorption and fluorescence, as well as the time-resolved fluorescence properties of dimethoxycurcumin and bis-dehydroxycurcumin dissolved in several solvents differing in polarity and H-bonding capability are presented. The singlet oxygen generation efficiency of the two compounds relative to curcumin is estimated. The photodegradation quantum yield of the former compound in acetonitrile and methanol is determined. The dimethoxycurcumin and bis-dehydroxycurcumin decay mechanisms from the S (1) state are discussed and compared with those of curcumin, dicinnamoylmethane and bis-demethoxycurcumin.

Evaluation of physicochemical properties and aggregation of the photosensitizers TPCS2a and TPPS2a in aqueous media.

Physicochemical properties of the novel photosensitizer meso-tetraphenyl chlorin disulphonate (TPCS2a) and the chemically related meso-tetraphenyl porphyrin disulphonate (TPPS2a) were investigated in aqueous solutions as part of pharmaceutical preformulation. Inflection points were calculated to be 3.9 for both compounds based on spectral shifts of aqueous solutions in the pH range 2-12, which likely correlate with indistinguishable pKa values of the imino nitrogens of the molecular cores. Accordingly, the fluorescence emission spectra showed pH dependent spectral shifts. Porphyrin-like compounds are known for aggregation in aqueous environments, and a small percentage of Tween 80 (0.006 % v/v = 4 x cmc) seemed to stabilize the aqueous samples of the two photosensitizers through hindrance of aggregation. The distribution coeffient of TPCS2a determined spectrophotometrically in 1-octanol/water is 0.4 (- 0.4 SD) and 1.5 (- 0.5 SD) for the reference TPPS2a. This confirms amphiphilicity which indicates preferred distribution and further restrain of diffusion in membranes, which is relevant for the use of TPCS2a as a photosensitizer in the process of photochemical internalization in vivo.

Solubilization of the novel anionic amphiphilic photosensitizer TPCS 2a by nonionic Pluronic block copolymers.

The influence of four nonionic Pluronic block copolymers (L44, F68, P123 and F127) on the solubilization and aggregation of the novel anionic amphiphilic photosensitizer TPCS(2a), intended for use in the technology of photochemical internalization (PCI), was evaluated in aqueous media as part of pharmaceutical preformulation studies. The evaluation was performed by use of UV-Vis spectroscopy for diluted samples of TPCS(2a) (3×10(-6)M), and capillary viscosimetry, freezing point depression measurements and atomic force microscopy (AFM) at pharmaceutical relevant concentrations (2; 10 or 30 mg/ml TPCS(2a)). The critical micelle concentration (CMC) of the Pluronics in presence of TPCS(2a) was determined spectrophotometrically. The Pluronic block copolymers solubilized the photosensitizer above CMC at ambient temperature by formation of vehicle-drug complexes apparently organized in networks of varying viscosity and morphology, which were sensitive towards the addition of neutral and charged excipients.

A screening of curcumin derivatives for antibacterial phototoxic effects studies on curcumin and curcuminoids. XLIII.

Curcumin, bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, has potential as a photosensitiser for photodynamic treatment of localised superficial infections in e.g., the mouth or skin. The aim of the present study was to evaluate the in vitro antibacterial phototoxic potential of a series of five curcumin derivatives. The gram-positive Enterococcus faecalis and the gram-negative Escherichia coli were used as bacterial models. The bacteria were exposed to curcuminoid preparations in two concentrations (2.5 and 25.0 microM) in combination with a constant irradiation dose (5 J/cm2). The UV-VIS absorption spectrum of the curcuminoids was in the same range as curcumin, 300-500 nm. Compound 1 (dimethoxycurcumin; C1) and compound 3 (bisdemethoxycurcumin; C3) were strongly phototoxic towards E. faecalis (no surviving bacteria) and showed a lower but significant effect towards E. coli (< or = 0.5 log reductions and 1 - 4 log reductions, respectively). Compound 2 (C2) and compound 4 (C4) in combination with blue light reduced the colony forming ability of E. faecalis (approximately 1-4 log reductions). The phototoxic effect of the curcuminoids varied with concentration, and for compounds C1, C2 and C3 it was further influenced by the addition of polyethylene glycol 400 (PEG 400) to the preparations. 2,6-Divanillylidenecyclohexanone (C5) showed very low phototoxic potential (< 0.2 log reductions) under the conditions used in the present study. The addition of polyethylene glycol 400 (PEG 400) seemed to increase the solubility of compound C1, C3 and C5 in phosphate buffered saline (PBS). This investigation demonstrates the importance and influence of the substituents on the phenolic rings and the keto-enol moiety for the phototoxic potential of curcumin and its derivatives.

Formulation and bacterial phototoxicity of curcumin loaded alginate foams for wound treatment applications: studies on curcumin and curcuminoides XLII.

Curcumin loaded alginate foams are proposed for application in antimicrobial photodynamic therapy of infected wounds. The drug loaded foams were formulated to provide a burst release of the photosensitizer when hydrated. The foams remained intact after hydration and would be possible to remove from the wound prior to irradiation without causing any tissue damage. The characterization of the prepared foams showed that both curcumin loaded and unloaded foams hydrated within 1 min and absorbed from 12 to 16 times their dry weight of a model physiological fluid. Curcumin, the model photosensitizer, has an extremely low solubility in water and may aggregate in aqueous environment. Cyclodextrins (CDs) and polyethylene glycol 400 (PEG 400) were therefore selected as solubilizers of curcumin in the foams to provide a burst release of the photosensitizer. Exposure to the prepared foams in combination with visible light irradiation (∼9.7 J/cm(2)) resulted in >6 log reduction of Entrococcus faecalis cells. However, curcumin mediated photokilling of Escherichia coli was ineffective when CDs were selected as solubilizer of curcumin in the foams. An 81% reduction in viable E. coli cells was detected after treatment with the foam containing PEG 400 as the only solubilizer of curcumin combined with visible light irradiation (∼29 J/cm(2)).

Physicochemical characterization of the photosensitizers TPCS2a and TPPS2a 1. Spectroscopic evaluation of drug--solvent interactions.

The spectroscopic properties of the patented photosensitizer meso-tetraphenyl chlorin disulphonate (TPCS2a), intended for use in photochemical internalization (PCI) technology, and the chemically related photosensitizer meso-tetraphenyl porphyrin disulphonate (TPPS2a) were characterized in 14 organic solvents of varying polarity and amphiprotic properties. Absorption spectra and fluorescence emission spectra were acquired, and Stokes' shifts and fluorescence quantum yields determined. These investigations yield information on the physicochemical interactions between the photosensitizers and their surroundings (i.e., the physiological environment in vivo or the vehicle in vitro), which is essential for the further development of drug formulations. TPPS2a and TPCS2a are rigid molecules, built up by conjugated ring systems which possess limited interactions with the surroundings in the ground state (So). Accordingly, only small spectral shifts were observed in the absorption spectra, as well as in the fluorescence emission spectra. TPPS2a is spatially more planar than TPCS2a, which is twisted as a result of reduction of a double bond in the core. However, the two compounds were quite similarly influenced by properties of the solvents, indicating that twisting has limited importance in the interactions of the two photosensitizers with their environment. Both compounds possess a high character of pi-pi* transition upon light exposure, supported by high molar absorption coefficients. The fluorescence quantum yields (phi(f)) were influenced by solvent properties to a larger extent than the spectral shifts. This might indicate that the reactivity of the first excited singlet state (S1*) significantly depends on the properties of the surroundings.

Photokilling of bacteria by curcumin in selected polyethylene glycol 400 (PEG 400) preparations. Studies on curcumin and curcuminoids, XLI.

Curcumin, bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, is a yellow-orange pigment which can be synthesised chemically or isolated from the plant Curcuma longa L. Curcumin has a rather broad absorption peak in the range 300-500 nm (maximum approximately 430 nm) and has potential as a photosensitiser for treatment of localised superficial infections in e.g., the mouth or skin. Previously, we have demonstrated phototoxic effects of curcumin in selected aqueous preparations against both gram-positive Enterococcus faecalis and Streptococcus intermedius and gram-negative Escherichia coil bacteria in vitro. One of the most efficient preparations was curcumin in polyethylene glycol (PEG 400) dissolved in phosphate buffered saline (PBS), pH 6.1. In this study the solubilising effect of PEG 400 on curcumin molecules and the in vitro phototoxic effects of these preparations were further evaluated. The effect of varying the curcumin concentration (2.50 microM -25.00 microM), the radiant exposure (0.5-30 J/cm2) and the physical state of curcumin against the survival of E. coli was investigated. PEG 400 showed an increasing physically stabilising effect towards crystallisation of curcumin in aqueous preparation with increasing concentrations (2.5%-10.0% v/v). Despite a higher solubility of curcumin with increasing PEG 400 concentrations, the surfactant reduced the phototoxicity of curcumin against E. coil. The highest phototoxic effect was obtained when curcumin was present in the least physically stable preparation, a stock solution in ethanol added to PBS with or without the lowest test concentration of PEG 400 (2.5% v/v). The obtained phototoxic effect can be increased by increasing the irradiation dose or by choosing an optimal curcumin concentration. E. faecalis was efficiently killed by the lowest concentration of curcumin in combination with the lowest radiant exposure when curcumin was dissolved in certain PEG solutions (< 0.02% survival), but showed no reduction when exposed to preirradiated curcumin.

Evaluation of novel alginate foams as drug delivery systems in antimicrobial photodynamic therapy (aPDT) of infected wounds--an in vitro study: studies on curcumin and curcuminoides XL.

The aim of the present study was to incorporate a model water-insoluble photosensitizer, curcumin, in novel alginate foams, further to evaluate the suitability of the curcumin loaded foams in antimicrobial photodynamic therapy of infected wounds. Six foam formulations were prepared and characterized with respect to physical characteristics, in vitro release and storage- and photo-stability of curcumin. One formulation was sterilized (gamma-sterilization). The foams contained hydroxypropyl-beta-cyclodextrins or hydroxypropyl-gamma-cyclodextrins as solubilizers of curcumin. A reference foam without cyclodextrins was prepared with PEG 400 as the solubilizer. At a curcumin load of 0.153% (w/w), the water insoluble photosensitizer was uniformly distributed in the hydrophilic foams matrix. All foams were easy to handle, flexible and hydrated rapidly in a model physiological fluid. Release of curcumin in its monomeric form was demonstrated in vitro and found to be dependent on the type and amount of cyclodextrins in the formulation. Curcumin was stable during storage, but susceptible to photodegradation in the foams, especially when the formulations contain PEG 400 or hydroxypropyl-gamma-cyclodextrins. Curcumin did not degrade after gamma-sterilization, however a decrease in the in vitro release rate of curcumin and changes in the foams physical characteristics were detected.

Lumichrome complexation by cyclodextrins: influence of pharmaceutical excipients.

Complexation of the model drug lumichrome by 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD), the most widely used cyclodextrin derivative in pharmaceutical preparations, was investigated in this study. The influence of frequently used pharmaceutical excipients, i.e. alcohols (ethanol, glycerol, propylene glycol), buffers (phosphate, citrate) and tonicity modulators (NaCl, MgCl2) was evaluated by phase solubility, absorption and fluorescence emission spectra and fluorescence lifetime studies. Further, complex formation constants and fluorescence quantum yields were calculated. The formation of a 1:1 complex was indicated by phase solubility studies. The shape of the absorption and emission spectra for lumichrome was nearly independent of dissolution medium. The intensity of the absorption peak was slightly decreasing by the addition of HPbetaCD, which indicates formation of an inclusion complex of lumichrome in the ground state. The intensity of the fluorescence emission peak (i.e. fluorescence quantum yield) was also steadily decreasing by the increase in HPbetaCD concentration. Monoexponential fluorescence decay was obtained in the absence of cyclodextrin. In the presence of cyclodextrin, bi-exponential decays were observed in all aqueous vehicles with the exception of plain water or samples containing salts. The longest decay time corresponds to the lifetime of free (uncomplexed) lumichrome, while the shortest decay time was attributed to the excited state of the complexed alloxazine form of lumichrome. The selected excipients influence the complexation constant and the lumichrome excited state deactivation pathways to various extents.

Photokilling of bacteria by curcumin in different aqueous preparations. Studies on curcumin and curcuminoids XXXVII.

Curcumin has potential as a photosensitiser (PS) in photodynamic therapy (PDT) for localised superficial infections. However, it is a challenge to make an optimal curcumin formulation in which curcumin has acceptable solubility and stability at physiological pH and combined with high selective phototoxic activity towards bacteria. In the present study, the phototoxic effects of curcumin against gram-negative and gram-positive bacteria were investigated in selected aqueous preparations. The gram-positive Enterococcus faecalis and Streptococcus intermedius and the gram-negative Escherichia coli were used as bacterial models. The bacteria were exposed to 1-25 microM curcumin solubilised in DMSO, cyclodextrines, liposomes and surfactants known to interfere with membranes. After 30 min incubation the bacteria were irradiated with fluorescent tubes emitting blue light (emission max 430 nm). The irradiance was 17 mW/cm2 and the radiant exposure (light dose) was 0.5-30J/cm2. The bacterial survival was calculated as a percentage compared to controls. Various post-irradiation incubation times were tested. Curcumin's native fluorescence was exploited in examination of curcumin uptake in or adherence to bacteria by fluorescence microscopy. Changes in post-irradiation incubation time, curcumin concentration, irradiation dose and preparation strongly influenced the phototoxic efficiency of curcumin in vitro. Aqueous preparations of DMSO, polyethyleneglycol and the pluronic block copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) were the most efficient vehicles for curcumin to exert photokilling of gram-positive and gram-negative bacteria.

Photoinduced color changes in two different qualities of riboflavin in the solid state and in various tablet formulations photoreactivity of biologically active compounds. XX.

There has been a gradual change in the relative amounts of synthetic and biosynthetic bulk riboflavin (RF) supplied to the overall market over the past years. The two sources of drug substance seem to have different photochemical properties that cannot be readily predicted. Alternating between the two qualities of RF therefore seems to influence the photochemical properties of the final product in a rather unpredictable way. A change in production method introduces the possibility of a change in polymorphic form which may alter the photoreactivity of the substance. The drug substance and tablets become green upon light exposure. The biosynthetic bulk material appears to be less photostable than the synthetic bulk material after inadvertent exposure to radiation or at elevated humidity. The observed color change cannot be explained by the formation of degradation products but is strongly dependent on the humidity level within the drug substance or preparation. The change in color was dramatically increased (by a factor up to 7) when the drug substance was formulated as tablets. Interactions were observed between RF and individual tablet components by mixing and compression at low pressure prior to exposure.

Investigation of curcumin-cyclodextrin inclusion complexation in aqueous solutions containing various alcoholic co-solvents and alginates using an UV-VIS titration method. Studies of curcumin and curcuminoides, XXXV.

The effect of pharmaceutical excipients like alcoholic co-solvents and water-soluble polymers on the inclusion complexation of curcumin in hydroxypropyl-beta-cyclodextrin and hydroxypropyl-gamma-cyclodextrin was investigated with a UV-VIS titration method. The association constants and the stoichiometries of the inclusion complexes in buffered media containing various amounts dl of alcoholic co-solvents and alginates were determined. The results showed a 1 : 1 stoichiometry between curcumin and both the cyclodextrins investigated in buffered media containing 10% (v/v) alcoholic co-solvents, although some 1 : 2 (host:guest) complexation was suspected between curcumin and hydroxypropyl-beta-cyclodextrin. The presence of 0.1% (w/v) sodium alginate or propylene glycol alginate did apparently not change the stoichiometry of the complexes formed. Curcumin was found to have a more than 30-fold higher association constant with hydroxypropyl-gamma-cyclodextrin compared to hydroxypropyl-beta-cyclodextrin in buffer containing 0.5% ethanol. Large variation in the association constants between curcumin and the cyclodextrins as a result of different co-solvents in the aqueous complexing media were found. A decrease in the association constant was seen as the chain lenght of the added co-solvent increased. Further, a decrease in the association constants was observed by addition of alginates in the case of hydroxypropyl-gamma-cyclodextrin at 0.5 or 5% (v/v) ethanol. The trend was opposite in the case of hydroxypropyl-beta-cyclodextrin, where a 30-90% increase in the association constant was observed in the presence of alginates. The results in the current study showed the large variations in the complexation between curcumin and hydroxypropyl-beta-cyclodextrin and hydroxypropyl-gamma-cyclodextrin, resepctively, as a result of various alcoholic co-solvents and alginates in the complexing media. The results also illustrated the importance of optimizing the solvent systems when utilizing cyclodextrins as drug carriers.