Stabilization of bovine insulin against agitation-induced aggregation using RNA aptamers

Insulin fibrillation: toward strategies for attenuating the process

The environmental factors affecting the rate of insulin fibrillation. The factors are representative.

Science and art of protein formulation development

Protein pharmaceuticals have become a significant class of marketed drug products and are expected to grow steadily over the next decade. Development of a commercial protein product is, however, a rather complex process. A critical step in this process is formulation development, enabling the final product configuration. A number of challenges still exist in the formulation development process. This review is intended to discuss these challenges, to illustrate the basic formulation development processes, and to compare the options and strategies in practical formulation development.

Challenges with osmolytes as inhibitors of protein aggregation: Can nucleic acid aptamers provide an answer?

Protein aggregation follows some common motifs. Whether in the formation of inclusion bodies in heterologous overexpression systems or inclusions in protein conformational diseases, or aggregation during storage or transport of protein formulations, aggregates form cross beta-sheet structures and stain with amyloidophilic dyes like Thioflavin T and Congo Red, irrespective of the concerned protein. Traditionally, osmolytes are used to stabilize proteins against stress conditions. They are employed right from protein expression, through production and purification, to formulation and administration. As osmolytes interact with the solvent, the differential effect of the stress condition on the solvent mostly determines the effect of the osmolyte on protein stability. Nucleic acid aptamers, on the other hand, are highly specific for their targets. When selected against monomeric, natively folded proteins, they bind to them with very high affinity. This binding inhibits the unfolding of the protein and/or monomer-monomer interaction which are the initial common steps of protein aggregation. Thus, by changing the approach to a protein-centric model, aptamers are able to function as universal stabilizers of proteins. The review discusses cases where osmolytes were unable to provide stabilization to proteins against different stress conditions, a gap which the aptamers seem to be able to fill.

Inhibition of insulin fibrillation by osmolytes: Mechanistic insights

We have studied here using a number of biophysical tools the effects of osmolytes, betaine, citrulline, proline and sorbitol which differ significantly in terms of their physical characteristics such as, charge distribution, polarity, H-bonding abilities etc, on the fibrillation of insulin. Among these, betaine, citrulline, and proline are very effective in decreasing the extent of fibrillation. Proline also causes a substantial delay in the onset of fibrillation in the concentration range (50–250 mM) whereas such an effect is seen for citrulline only at 250 mM, and in case of betaine this effect is not seen at all in the whole concentration range. The enthalpies of interaction at various stages of fibrillation process have suggested that the preferential exclusion of the osmolyte and its polar interaction with the protein are important in inhibition. The results indicate that the osmolytes are most effective when added prior to the elongation stage of fibrillation. These observations have significant biological implications, since insulin fibrillation is known to cause injection amyloidosis and our data may help in designing lead drug molecules and development of potential therapeutic strategies.

Nucleic acid aptamers stabilize proteins against different types of stress conditions

It has been observed that the same osmolyte cannot provide protection to a protein exposed to more than one stress condition. We wanted to study the effect of nucleic acid aptamers on the stabilization of proteins against a variety of stress conditions. Adjuvanted tetanus toxoid was exposed to thermal, freeze-thawing, and agitation stress. The stability and antigenicity of the toxoid were measured. Using nucleic acid aptamers selected against tetanus toxoid, we show that these specific RNA sequences were able to stabilize alumina-adsorbed tetanus toxoid against thermal-, agitation-, and freeze-thawing-induced stress. Binding affinity of the aptamer-protein complex did not show any significant change at elevated temperature as compared with that at room temperature, indicating that the aptamer protected the protein by remaining bound to it under stress conditions and did not allow either the protein to unfold or to promote protein-protein interaction. Thus, we show that by changing the stabilization strategy from a solvent-centric to a protein-centric approach, the same molecule can be employed as a stabilizer against more than one stress condition and thus probably reduce the cost of the product during its formulation.