Inulin glasses for the stabilization of therapeutic proteins

Sugar glasses are widely used to stabilize proteins during drying and subse quent storage. To act successfully as a protectant. the sugars should have a high glass transition temperature (Tg). a poor hygroscopicity, a low crys tallization rate, and contain no reducing groups. When freeze drying is env isaged as method of drying, a relatively high Tg of the freeze concentrated fraction (Tg') is preferrable. in this study, whether inulins meet these r equirements was investigated. Inulins of various degrees of polymerisation (DP) were evaluated. Trehalose glass was used as a positive control. It was found that the Tg and the Tg' of inulins with a number/weight average DP ( DPn/DPw) higher than 5.5/6.0 were higher than those of trehalose glass. Fur thermore, inulin glasses showed a similar hygroscopicity to that of trehalo se glass but crystallized less rapidly. Less than 6% of the sugar units of inulins with a DPn/DPw higher than 5.5/6.0 contained reducing groups. Treha lose contained no reducing groups. Freeze drying of an alkaline phosphatase solution without protectant induced an almost complete loss of the activit y of the protein. In contrast, when inulins with a DPn/DPw higher than 5.5/ 6.0 or trehalose were used as stabilizer, the activity was fully maintained , also after subsequent storage for 4 weeks at 20 degreesC and 0, 45, or 60 % RH, respectively. The stabilizing capacities of inulin with a lower DP an d glucose were substantially less pronounced. After storage at 60 degreesC for 6 days, the activity of freeze dried samples containing inulins with a DPn/DPw higher than 5.5/6.0 was still about 50% whereas the activity of sam ples containing inulin with a lower DP, glucose, or trehalose was completel y lost. It is: concluded that inulins with a DPn/DPw higher than 5.5/6.0 me et the physicochemical characteristics to successfully act as protectants f or proteins. The stabilizing potential of these inulins was clearly shown u sing alkaline phosphatase as a model protein. (C) 2001 Elsevier Science B.V . All rights reserved.