Assessment of current protocols for the production of therapeutic gonadotropins

Gonadotropins are in demand because of their therapeutic potential in assisted reproductive technologies. Purification from urine, blood and pituitaries has been the preferred method till now. Extraction, bulk fractionation followed by fine separation has been the general approach. Micro-heterogeneity has been a bane for endocrinologists involved in purification of these hormones. Charge isoforms and size isoforms have been the major micro-heterogeneous forms of gonadotropins. In some cases i.e. human and farm animal gonadotropins differential charge based micro-heterogeneity has been ascribed to differential degree of sulfation or sialylation. Charge isoforms have been separated and purified in bulk by appropriate ion exchange chromatography. Differential glycosylation has also been observed to result in micro-heterogeneity. Lectin based affinity chromatography can separate many Such isoforms. Other micro-heterogeneous forms like free subunits and their aggregates, oligomers of the native heterodimer hormones and peptide bond nicked hormones have also been observed. One possible reason for low yield of gonadotropin could be that, isoforms were getting differentially distributed in different side fractions'. Group reactive affinity methods have been employed in obtaining enriched preparations containing all the isoforms. Special down stream processing techniques have to be developed for purification of recombinant gonadotropins. Synthetic superactive gonadotropin analogues have also been produced and purified. All the different forms of gonadotropins, natural and synthetic are extremely useful however, for structure-function relationship studies even though they pose technical challenge for purification.