The user safety assessment of a selenized yeast feed additive.

Purpose: Of the several selenized yeasts authorised for use as feed additives in the EU, Saccharomyces cerevisiae CNCM I-3060 inactivated' (Sel-Plex®), was the first to be approved for use, in 2006. The additive has a concentration of selenium between 2000 and 2400 mg/kg and a selenomethionine content greater than 63%. Previous toxicological and safety studies have shown Sel-Plex® to be safe for use for target animal species, consumers, users and the environment. A new formulation of Sel-Plex® was recently developed however, with a minimum selenium content of 3000 mg/kg. The increase in selenium in this product, Sel-Plex® 3000, presented the need to assess the risk for workers and users and to establish if there would be any eye and/or skin irritancy and skin sensitisation effects associated with the product. The purpose of this paper is to present the methodology and results of the user safety skin and eye studies performed on Sel-Plex® 3000.Materials & Methods: In vitro skin and eye models were used to assess skin and eye irritancy, while skin sensitisation was examined using an in vivo method. The acute eye irritation was evaluated using a Reconstructed human Cornea-like Epithelium (RhCE) model, which followed the OECD guideline 492. The skin irritation was assessed based on its ability to induce cell death in a commercial reconstructed human epidermis (RhE) model (EPISKIN™) according to the OECD Guideline No. 439. The skin sensitising potential was evaluated in the Guinea pig in line with OECD Guideline 406, and measured the extent and degree of skin reaction to a challenge exposure following previous topical exposure of a substance on the skin.Results: The skin and eye irritation test results showed that Sel-Plex® 3000 was a non-irritant in both cases. The skin sensitisation study showed that the additive did not generate a sensitisation response in the guinea pig and should not be considered a skin sensitiser.Conclusion: These results indicate that Sel-Plex® 3000 is safe to use for workers in an industrial setting when handling the product and the studies may be further used to support regulatory compliance in respective markets.

Novel isosorbide di-ester compounds as inhibitors of acetylcholinesterase.

We report herein that a variety of isosorbide di-esters, previously reported to be novel substrates for butyrylcholinesterase (BuChE, EC 3.1.1.8), are in fact inhibitors of the homologous enzyme acetylcholinesterase (AChE), with IC(50) values in the micromolar range. In vitro studies show that they are mixed inhibitors of the enzyme, and thus the ternary enzyme-inhibitor-substrate complex can form in acetylcholinesterase. This is rationalised by molecular modelling which shows that the compounds bind in the mid-gorge area. In this position, simultaneous substrate binding might be possible, but the hydrolysis of this substrate is prevented. The di-esters dock within the butyrylcholinesterase gorge in a very different manner, with the ester sidechain at the 5-position occupying the acyl pocket at residues Leu286 and Val288, and the 2-ester binding to Trp82. The carbonyl group of the 2-ester is susceptible to nucleophilic attack by Ser198 of the catalytic triad. The larger residues of the acyl pocket in acetylcholinesterase prevent binding in this manner. The results complement each other and explain the differing behaviours of the esters in the cholinesterase enzymes. These findings may prove very significant for future work.