Nanoscale Lipophilic Prodrugs of Dexamethasone with Enhanced Pharmacokinetics

The encapsulation of glucocorticoids, such as dexamethasone, in nanoparticles (NPs) faces two main issues: a low drug loading and the destabilization of the nanoparticle suspension due to drug crystallization. Here, we successfully formulated a prodrug of dexamethasone, dexamethasone palmitate (DXP), into nanoparticles stabilized by the sole presence of distearoyl- sn-glycero-3-phosphoethanolamine- N-[methoxy(poly(ethylene glycol))-2000] (DSPE-PEG₂₀₀₀). Two formulation processes, nanoprecipitation and emulsion-evaporation, allowed the formation of stable nanoparticles. By adjusting the drug/lipid ratio and the DXP concentration, nanoparticles of DXP (DXP-NPs) with a size between 130 and 300 nm can be obtained. Owing to the presence of DSPE-PEG₂₀₀₀, a high drug entrapment efficiency of 98% w/w was reached for both processes, corresponding to a very high equivalent dexamethasone drug loading of around 50% w/w in the absence of crystallization upon storage at 4 °C. The anti-inflammatory activity of DXP-NPs was preserved when incubated with macrophages activated with lipopolysaccharide. Pharmacokinetics parameters were evaluated after intravenous (IV) injection of DXP-NPs to healthy mice. The release of DXM from DXP-NPs in plasma was clearly controlled up to 18 h compared with the free drug, which was rapidly eliminated from plasma after administration. In conclusion, a novel type of nanoparticle combining the advantages of prodrugs and nanoparticles was designed, easy to produce with a high loading efficiency and leading to modified pharmacokinetics and tissue distribution after IV administration.

Density functional theory and liquid chromatography-multistage mass spectrometry to characterize raltitrexed photo-degradation mechanisms

The structure of raltitrexed photoproducts was elucidated by LC-ESI-HR-MSⁿ. Photodegradation pathways are proposed, using DFT approach to support assumptions. Ralitrexed photodegrades as per photosensitization mechanisms.

Electrostatic Potential from High-Resolution X-Ray Diffraction. Application to a Pseudo-Peptide Molecule

The calculation of the electrostatic potential of a molecule removed from the crystal lattice is derived from the parameters obtained by a kappa refinement and by a Hansen-Coppens electron density model. These calculations in direct space are applied to N-acetyl-α,β-dehydrophenylalanine; deformation potentials calculated by Fourier transformation are compared to those obtained in direct space.

Experimental and database-transferred electron-density analysis and evaluation of electrostatic forces in coumarin-102 dye

The electron-density distribution of a new crystal form of coumarin-102, a laser dye, has been investigated using the Hansen-Coppens multipolar atom model. The charge density was refined versus high-resolution X-ray diffraction data collected at 100 K and was also constructed by transferring the charge density from the Experimental Library of Multipolar Atom Model (ELMAM2). The topology of the refined charge density has been analysed within the Bader `Atoms In Molecules' theory framework. Deformation electron-density peak heights and topological features indicate that the chromen-2-one ring system has a delocalized π-electron cloud in resonance with the N (amino) atom. The molecular electrostatic potential was estimated from both experimental and transferred multipolar models; it reveals an asymmetric character of the charge distribution across the molecule. This polarization effect is due to a substantial charge delocalization within the molecule. The molecular dipole moments derived from the experimental and transferred multipolar models are also compared with the liquid and gas-phase dipole moments. The substantial molecular dipole moment enhancements observed in the crystal environment originate from the crystal field and from intermolecular charge transfer induced and controlled by C-H···O and C-H···N intermolecular hydrogen bonds. The atomic forces were integrated over the atomic basins and compared for the two electron-density models.

Backbone side chain interactions in peptides. I. Crystal structures of model dipeptides with the Pro-Ser sequence

The preferential occurrence of amino-acid residues having short polar side-chain within beta-folded regions of crystallized proteins suggests the existence of some stabilizing interaction involving the side polar function. Three model dipeptides tBuCO-L-Pro-L-Ser-NHMe 1, tBuCO-L-Pro-D-Ser-NHMe 2 in the pure enantiomeric a and racemic b forms, and iPrCO-L-Pro-D-Ser-OMe 3 have been investigated in the solid state by X-ray crystallography. Homo and heterochiral sequences 1 and 2 are folded in the beta I and beta II types, respectively, whereas 3 obviously accommodates an open conformation. Besides the i + 3 leads to i hydrogen bond typical of beta-bends in 1, 2a, and 2b, the Ser NH group in all four crystal structures is a proton donor to the lone orbitals of the Ser O gamma oxygen atom. The result is that the disposition of the Ser C alpha--C beta bond corresponds to the rotamer III (chi 1 congruent to 60 degrees). As shown by the crystal structure of 3, the intra-Ser NH. . .O gamma hydrogen bonding is not restricted to beta-folded Pro-Ser sequences. Therefore, this interaction is not only a stabilizing factor for beta-turns but it is also probably responsible for the already mentioned stability of rotamer III for the Ser C alpha--C beta bond in peptides and protein.