Solubilization of the chlorin TPCS2a in the presence of Pluronic® F127/Tween 80 mixtures.

The efficacy of surfactant mixtures of Pluronic® F127 and Tween 80 at overall concentration in the micromolar range and molar ratio 1:1, 1:10, and 10:1 in inhibiting aggregation of the photosensitizer meso-tetraphenyl chlorin disulphonate (TPCS2a) was investigated in aqueous media at pH 2.9 by means of steady-state absorption and fluorescence emission spectroscopy as well as time-resolved fluorescence analysis. Corresponding experiments were performed at pH 7.4 in the absence of surfactants to determine the spectroscopic properties of a monomeric sample. Aggregation resulted in a red shift of the Soret absorption band and in substantial fluorescence quenching. The fluorescence lifetime of TPCS2a was a particularly sensitive indicator of the aggregation state, as the monomer at pH 7.4 decayed with a ∼ 10 ns time constant, while aggregation resulted in subnanosecond decay. The critical micelle concentration (CMC) of the surfactant mixtures was determined spectrophotometrically in the presence of TPCS2a. The ability of the surfactant mixtures to prevent aggregation at acidic pH was evaluated at overall surfactant concentration below and above CMC. Solubilization of TPCS2a in Pluronic® F127/Tween 80 mixtures prevented aggregation of the photosensitizer at overall surfactant concentrations much lower than those needed for both pure Pluronic® F127 and pure Tween 80.

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, ß, 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 HPßCD. 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.

Studies on curcumin and curcuminoids. XXXIV. Photophysical properties of a symmetrical, non-substituted curcumin analogue.

Curcumin is the main constituent of curry. In its ground state it shows chemo-preventive, chemo-therapeutic, anti-inflammatory and immune stimulating effects, and it is considered as a drug or drug model in the treatment of AIDS and cystic fibrosis. Further biological activity is induced in curcumin by light exposure: cytotoxicity is enhanced and photosensitized antibacterial effects are achieved. For the curcumin cis enol conformer, the fastest deactivation mechanism of the first excited singlet state is an excited-state intra-molecular proton transfer, which brings curcumin back to the ground state. This mechanism, as well as reketonization, interaction with the solvent and photodegradation, compete with the phototherapeutic action. The native compound curcumin carries phenolic hydroxyl and methoxy groups that influence the molecular charge distribution and hence the excited-state intra-molecular proton transfer rate in an unpredictable way. In this work we study static and time-resolved spectroscopic properties of a non-substituted curcuminoid that lacks both the phenolic hydroxyl and the phenolic methoxy groups. The photophysical properties of this compound are compared to those of native curcumin, in order to provide a rationale to the design of curcuminoids with molecular structures optimized for a photosensitizer.

Intranasal midazolam: a comparison of two delivery devices in human volunteers.

Bidirectional nasal drug delivery is a new administration principle with improved deposition pattern that may increase nasal drug uptake. Twelve healthy subjects were included in this open, non-randomized 3-way crossover study: midazolam (3.4 mg) intravenously (1 mg mL (-1)), or nasally by bidirectional or traditional spray (2 x100 microL of a 17 mg mL(-1) nasal midazolam formulation). The primary outcome was bioavailability. Blood samples were drawn for 6 h for determination (gas-chromatography-mass-spectrometry) of midazolam and 1-OH-midazolam. Pharmacokinetic calculations were based on non-compartmental modelling, sedation assessed by a subjective 0-10 NRS-scale, and nasal dimensions by non-invasive acoustic rhinometry. Mean bioavailabilities were 0.68-0.71, and Tmax 15 min for the sprays, which also were bioequivalent (ratio geometric means (90%) CI: 97.6% (90% CI 83.5; 113.9)). Sedation after bidirectional spray followed intravenous sedation closely, while sedation after the traditional spray was less pronounced. A negative correlation between Cmax and smallest cross-sectional area was seen. Adverse effects such as local irritation did not differ significantly between the sprays. Apparently bidirectional delivery did not increase systemic bioavailability of midazolam. We cannot disregard that only the traditional spray caused less sedation than intravenous administration. This finding needs to be confirmed in trials designed for this purpose.