On the impact of ethanol on the rejection and transfer mechanism during ultrafiltration of a charged macromolecule in water/ethanol.

Ultrafiltration (UF) is a sustainable membrane separation technique. It could be useful for the concentration/purification of bio-sourced molecules that are extracted either by pure ethanol or by water/ethanol mixtures. Nevertheless, the process optimization requires an in-depth understanding of the transfer mechanisms of solute through membranes, especially for charged solutes, that are nowadays not sufficiently documented. Previous studies achieved in aqueous media have shown that the rejection of charged solutes by an UF membrane involves at least three mechanisms: convection, diffusion and electrostatic interactions. The present study aims at a systematic analysis of the transfer mechanisms of a model protein (lysozyme) in water/ethanol mixtures (100/0-70/30 v/v) during UF by a zirconia inorganic membrane. The influence of the pH varying in the 4-9 range and of the ionic strength (I) is also discussed. The ionic strength I can be adjusted by addition of an indifferent electrolyte (NaCl) only aiming at the screening of the electrostatic interactions or by addition of a selectively adsorbed electrolyte(KH2PO4) that is able to change the isoelectric pH of the protein and thus to modulate the electrostatic interactions in a different way when compared to NaCl. Of course, both salts have an impact on the protein rejection in UF. The results are analysed using the CDE model previously developed in our group to explain the behaviour of a single protein during UF in water and accounting for convection, diffusion and electrophoretic migration. The applicability of the CDE model in water/ethanol mixtures up to 70/30 v/v is finally shown.

Endocrine sequelae of childhood craniopharyngioma.

The endocrine sequelae of 62 children with craniopharyngioma were studied retrospectively. These patients were followed for a median duration of 3 years (range 1 to 10 years). Eighteen patients had a long-term follow-up for more than 5 years (range 5 to 10 years). Complete surgical resection was achieved in 30 patients and 32 patients had residual tumor. Twenty-five patients had recurrence or progression of the residual tumor and were treated with radiotherapy. Presenting complaints suggestive of endocrinopathy were infrequent. The most common presenting symptoms were headache, nausea and vomiting, followed by growth failure. Pre-operatively, growth hormone deficiency was the most commonly encountered pituitary hormonal deficiency; however postoperatively, most children had diabetes insipidus. Multiple pituitary hormonal deficiencies were more frequently observed in children treated with extensive radical surgery than in those treated with conservative surgery and radiotherapy. The endocrine morbidity associated with craniopharyngioma and its different management modalities remains high; however, it is manageable with appropriate hormonal replacement therapy.

Mechanism-based inhibition of proline dehydrogenase by proline analogues.

The inactivation of proline dehydrogenase by several L-Pro analogues was investigated with the aim to block the essential metabolic pathway of tsetse flies allowing the degradation of L-Pro to L-Glu. In vitro studies on rat liver mitochondria showed that only 4-methylene-L-proline was able to inactivate proline dehydrogenase. The inactivation kinetics agreed with a mechanism-based inhibition. The other tested analogues E- and Z-4-fluoromethylene-L-proline, and cis and trans-5-ethynyl-D,L-proline were neither substrate nor inactivator of the enzyme. In vivo 4-methylene-L-proline showed no toxicity against Drosophila flies, but was lethal for Glossina pallidipes flies. This result allows the consideration of 4-methylene-L-proline as an attractive compound molecule in the struggle against tsetse flies.