A dynamic mechanical method for determining the silicone elastomer solubility of drugs and pharmaceutical excipients in silicone intravaginal drug delivery rings

The silicone elastomer solubilities of a range of drugs and pharmaceutical excipients employed in the development of silicone intravaginal drug delivery rings (polyethylene glycols, norethisterone acetate, estradiol, triclosan, oleyl alcohol, oxybutynin) have been determined using dynamic mechanical analysis. The method involves measuring the concentration-dependent decrease in the storage modulus associated with the melting of the incorporated drug/excipient, and extrapolation to zero change in storage modulus. The study also demonstrates the effect of drug/excipient concentrations on the mechanical stiffness of the silicone devices at 37°C.

High speed DSC (hyper-DSC) as a tool to measure the solubility of a drug within a solid or semi-solid matrix

Conventional differential scanning calorimetry (DSC) techniques are commonly used to quantify the solubility of drugs within polymeric-controlled delivery systems. However, the nature of the DSC experiment, and in particular the relatively slow heating rates employed, limit its use to the measurement of drug solubility at the drug's melting temperature. Here, we describe the application of hyper-DSC (HDSC), a variant of DSC involving extremely rapid heating rates, to the calculation of the solubility of a model drug, metronidazole, in silicone elastomer, and demonstrate that the faster heating rates permit the solubility to be calculated under non-equilibrium conditions such that the solubility better approximates that at the temperature of use. At a heating rate of 400 degrees C/min (HDSC), metronidazole solubility was calculated to be 2.16 mg/g compared with 6.16 mg/g at 20 degrees C/min. (C) 2005 Elsevier B.V. All rights reserved.

Inhibition and fibril formation and toxicity of a fragment of alpha-synuclein by an N-methylated peptide analogue

Alpha-synuclein has been linked to amyloidogenesis in Parkinson's disease and other neurodegenerative disorders. We have previously shown that a peptide comprising residues 68-78 of alpha-synuclein is the minimum fragment that, like alpha-synuclein itself, forms amyloid fibrils and exhibits toxicity towards cells in culture. Hughes et al. [J. Biol. Chem. 275 (2000) 25109] showed that an N-methylated derivative of Abeta(25-35) inhibited the formation of fibrils by Abeta(25-35) and reduced its toxicity. We have now extended this concept to an amyloidogenic alpha-synuclein-based peptide. Alpha-synuclein(68-78), N-methylated at G1y73, was compared to non-methylated peptide. Whereas alpha-synuclein(68-78) formed fibrils and was toxic to cells, the N-methylated analogue had neither of these properties. Moreover, an equimolar mixture of the non-methylated and methylated peptides formed very few fibrils and toxicity was markedly reduced.

Identification of the region of non-A beta component (NAC) of alzheimer's disease amyloid responsible for its aggregation and toxicity

The non-beta-amyloid (Aß) component of Alzheimer's disease amyloid (NAC) and its precursor a-synuclein have been linked to amyloidogenesis in several neurodegenerative diseases. NAC and a-synuclein both form ß-sheet structures upon ageing, aggregate to form fibrils, and are neurotoxic. We recently established that a peptide comprising residues 3±18 of NAC retains these properties. To pinpoint the exact region responsible we have carried out assays of toxicity and physicochemical properties on smaller fragments of NAC. Toxicity was measured by the ability of fresh and aged peptides to inhibit the reduction of the redox dye 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) by rat pheochromocytoma PC12 cells and human neuroblastoma SHSY-5Y cells. On immediate dissolution, or after ageing, the fragments NAC(8±18) and NAC(8±16) are toxic, whereas NAC(12±18), NAC(9±16) and NAC(8±15) are not. Circular dichroism indicates that none of the peptides displays ß-sheet structure; rather all remain random coil throughout 24 h. However, in acetonitrile, an organic solvent known to induce ß sheet, fragments NAC(8±18) and NAC(8±16) both form ß-sheet structure. Only NAC(8±18) aggregates, as indicated by concentration of peptide remaining in solution after 3 days, and forms fibrils, as determined by electron microscopy. These findings indicate that residues 8±16 of NAC, equivalent to residues 68±76 in a-synuclein, comprise the region crucial for toxicity.