Separation of oxidized variants of a monoclonal antibody by anion-exchange

Monoclonal antibodies are subject to a variety of degradation mechanisms, therefore orthogonal techniques are required to demonstrate product quality. In this study, the three individual antibodies comprising a multi-antibody drug product, XOMA 3AB were evaluated by both cation-exchange (CEX) and anion-exchange chromatography (AEX). In contrast to CEX analysis which showed only a single, broad peak for the force-oxidized antibodies, AEX analysis of Ab-A (pI=7.6) revealed two more basic peaks. Ab-B (pI=6.7) bound but exhibited only a single major peak while Ab-C (pI=8.6) flowed through. Peptide mapping LC/MS analysis of the isolated Ab-A fractions demonstrated that the basic peaks resulted from oxidation in a complementary determining region (CDR). Differential scanning calorimetry (DSC) analysis of the oxidized Ab-A species showed a decrease in the Fab melting point for the oxidized species consistent with unfolding of the molecule. Greater/lesser surface exposure of ionic residues resulting from a conformational change provides a likely explanation for the dramatic shift in retention behavior for the Ab-A oxidized variants. Peptide mapping analysis of the Ab-B antibody showed, in contrast to Ab-A, no detectable CDR oxidation. Hence, the lack of separation of oxidized variants in Ab-B can be explained by the absence of CDR oxidation and the associated changes in secondary/tertiary structure which were observed for oxidized Ab-A. In summary, anion-exchange HPLC shows potential as an orthogonal analytical technique for assessing product quality of monoclonal antibody therapeutics. In the case of the XOMA 3AB drug product, two of the antibodies bound and one, Ab-A, exhibited separation of CDR oxidized variants.     

Fatty acid composition of two Athamanta turbith subspecies

The fruit oils of Athamanta turbith ssp. hungarica and Athamanta turbith ssp. haynaldii were obtained by Soxhlet extraction using petroleum ether. The fatty acid composition of oils was determined by GC in the methyl ester form. Considering the composition and content of fatty acids, the examined oils were very similar. Petroselinic acid was the principal one (45.6 and 46.2%, respectively), followed by a significant amount of linoleic acid (26.9 and 29.1%, respectively). In both oils, myristic, pentadecanoic, palmitic, palmitoleic, stearic, petroselinic, oleic, linoleic, α-linolenic, arachidic, and behenic acid were identified. Lignoceric acid was detected only in A. turbith ssp. hungarica oil. Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 319–320, July–August, 2006.     

Conductivity of water-in-oil microemulsions: Comparison of the Boltzmann statistics and the charge fluctuation model

The electrical conductivity of water-in-oil microemulsions is interpreted on the basis of the distribution of ionic charges among the droplets. The charging energy is approximated by the Born energy. In the interpretation, the hydrodynamic radius is distinguished from the water core radius. The Boltzmann statistics are compared with the fluctuation theory. The former approach is more realistic due to its consideration of the discrete nature of charge, while the latter better fits the data obtained with the AOT-water-isooctane system.