Rheological and syringeability properties of highly concentrated human polyclonal immunoglobulin solutions.

This study of highly concentrated polyvalent immunoglobulin solutions, IgG, aimed at analyzing the relationships between protein concentration and aggregation on the one hand and viscosity on the other hand. Viscosity variations as a function of IgG concentration showed two well-defined behaviours: a Newtonian behaviour for low-concentrated solutions and a shear-thinning behaviour for highly concentrated ones. The viscosity data fitted very well with the Mooney model, suggesting the absence of intermolecular interactions in the IgG solutions that behaved like a non-interacting suspension of hard particles. The polyclonal nature of IgG seems to prevent intermolecular interaction. The shape factor, determined from Mooney fitting, revealed a non-spherical shape of the polyclonal IgG molecules. The rheological properties were also correlated with the injection force (F) through hypodermic needles by syringeability tests. Here, F was mainly affected by three parameters: the solution viscosity, the injection flow rate, and the needle characteristics. In fact, syringeability tests showed that F increased with IgG concentration and flow rate and decreased with the internal diameter of the needle. A zone for optimal injection conditions was then identified taking into account the different affecting parameters and mainly a maximum force for manual injection, which was fixed at 30N.

DNA compaction into new DNA vectors based on cyclodextrin polymer: surface enhanced Raman spectroscopy characterization.

The ability of DNA to bind polycation yielding polyplexes is widely used in nonviral gene delivery. The aim of the present study was to evaluate the DNA compaction with a new DNA vector using Raman spectroscopy. The polyplexes result from an association of a beta-cyclodextrin polymer (polybeta-CD), an amphiphilic cationic connector (DC-Chol or adamantane derivative Ada2), and DNA. The charge of the polymeric vector is effectively controlled by simple addition of cationic connector in the medium. We used surface enhanced Raman spectroscopy (SERS) to characterize this ternary complex, monitoring the accessibility of adenyl residues to silver colloids. The first experiments were performed using model systems based on polyA (polyadenosine monophosphate) well characterized by SERS. This model was then extended to plasmid DNA to study polybeta-CD/Ada2/DNA and polybeta-CD/DC-Chol/DNA polyplexes. The SERS spectra show a decrease of signal intensity when the vector/DNA charge ratio (Z+/-) increases. At the highest ratio (Z+/- = 10) the signal is 6-fold and 3-fold less intense than the DNA reference signal for Ada2 and DC-Chol polyplexes, respectively. Thus adenyl residues have a reduced accessibility as DNA is bound to the vector. Moreover, the SERS intensity variations are in agreement with gel electrophoresis and zeta potential experiments on the same systems. The overall study clearly demonstrates that the cationic charges neutralizing the negative charges of DNA result in the formation of stable polyplexes. In vitro transfection efficiency of those DNA vectors are also presented and compared to the classical DC-Chol lipoplexes (DC-Chol/DNA). The results show an increase of the transfection efficiency 2-fold higher with our vector based on polybeta-CD.