Pharmaceutical Research, Vol. 21, No. 12, December 2004 Effects of Hydrophilic Cyclodextrins on Aggregation of Recombinant Human Growth Hormone Sumitra Tavornvipas, Shinichiro Tajiri,　Fumitoshi Hirayama, Hidetoshi Arima, and　Kaneto Uekama Purpose. To evaluate the effect of hydrophilic cyclodextrins (CyDs) on the aggregation induced by different stresses and on the oxidation and deamidation of recombinant human growth hormone (rhGH). Methods. The aggregation of rhGH was induced by three denaturing techniques including chemical (4.5 M guanidine hydrochloride), thermal (differential scanning calorimetry), and interfacial denaturation (vortex agitation). The aggregates were characterized and quantified by UV spectrophotometry and size exclusion chromatography. The effects of hydrophilic CyDs on deamidation and oxidation rates of rhGH were studied by HPLC method. Results. In both thermally and chemically induced aggregations, branched β-CyDs significantly inhibited the aggregation of rhGH compared with the other α- and γ-CyDs. This can explain that the β-CyD cavity with branched sugar moieties may be relatively preferable in preventing the aggregation of rhGH. In contrast, 2-hydroxypropyl β -CyD with surface activity was found to be effective in reducing the aggregation induced by interfacial denaturation compared with those of branched β-CyDs. On the other hand, these hydrophilic CyDs showed no noticeable inhibitory effect on the oxidation and deamidation rates of rhGH. The results suggested that CyDs interact preferably with exposed hydrophobic side chains rather than aliphatic side chains of rhGH, resulting in the inhibition of aggregation but not the oxidation and deamidation rates. Conclusions. The different inhibitory effect of CyDs is dependent not only on the structure and property of CyD itself but also the nature of the denaturing stimulus. The current results suggested that hydrophilic β-CyDs can effectively inhibit the aggregation of rhGH. Thus, hydrophilic β-CyDs may be potentially useful excipients for parenteral preparation of rhGH.