Moisture Content and Molecular Mobility

The chemical and physical stability of peptides and proteins in the solid state is largely affected by moisture content. Freeze-dried ribonuclease A with a higher water content exhibited a greater extent of aggregation, as shown in Fig. 202.847 The effect of water content on protein stability has also been reported for lyophilized human growth hormone825,848 and a lyophilized monoclonal antibody-vinca conjugatew9 among others.

Moisture absorption often decreases storage stability of lyophilized proteins; however, extremely low moisture content can also decrease storage stability. The optimum residual

0.20

0 20 40 60 80 100 120

storage time (day)

Figure 202. Effect of water content on the aggregation of freeze-dried ribonuclease A at 45°C. Moisture content: approximately 125 mol (a) and 700 mol (b) of H2O per mole of enzyme. (Reproduced from Ref. 847 with permission.)

moisture in lyophilized tissue-type plasminogen activator was consistent with the minimum amount of moisture necessary to shield strongly polar groups in protein molecules.850 A similar effect of water content on protein stability was reported for lyophilized billirubin oxidase.851

Destabilization caused by excess moisture absorption has been demonstrated with various lyophilized proteins. Storage of freeze-dried insulin at high relative humidity caused, as expected, a higher moisture absorption, which then resulted in increased aggregation, as shown in Fig. 203.810 Aggregation of freeze-dried bovine serum albumin via disulfide bond formation increased with increasing water content (Fig. 204).807852 Aggregation of lyophilized P-galactosidase and bovine serum albumin in solution also increased with increasing water content.809 853 Destabilization caused by moisture absorption can be ascribed to the plasticizing effect of water, which increases the molecular mobility of Iyophiles. Plasticiza-tion of lyophilized P-galactosidase and bovine serum albumin due to moisture absorption was accompanied by an increase in the mobility of water molecules as measured by the spin-lattice relaxation time of H217O.809 853

Plasticization due to moisture absorption also increases the mobility of protein molecules themselves. The molecular mobility of freeze-dried bovine serum y-globulin, as

Dryed Bovine Serum

Figure 203. Relationship between moisture adsorption (a) and aggregation (b) for freeze-dried insulin stored at 50°C for 24 h. (Reproduced from Ref. 810 with permission.)

Figure 203. Relationship between moisture adsorption (a) and aggregation (b) for freeze-dried insulin stored at 50°C for 24 h. (Reproduced from Ref. 810 with permission.)

amount of water added (til)

Figure 204. Effect of added water content on the aggregation of freeze-dried bovine serum albumin stored at 37°C for 24 h. [From W. R. Liu, R. Langer, and A. M. Klibanov, Moisture-induced aggregation of lyophilized proteins in the solid state, Biotechnol. Bioeng. 37,177-184 (1991). Reproduced by permission of Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc.]

amount of water added (til)

Figure 204. Effect of added water content on the aggregation of freeze-dried bovine serum albumin stored at 37°C for 24 h. [From W. R. Liu, R. Langer, and A. M. Klibanov, Moisture-induced aggregation of lyophilized proteins in the solid state, Biotechnol. Bioeng. 37,177-184 (1991). Reproduced by permission of Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc.]

measured by the spin-spin relaxation time of protein protons, increased with increasing water content, resulting in enhanced aggregation.854 The critical temperature of appearance of liquidlike protons with higher mobility in lyophilized proteins ( Tmc), detected by NMR relaxation measurements, was closely related to protein stability, such that protein aggregation became measurable on the experimental time scale at temperatures above the critical temperature.855 A decrease in TiC upon moisture absorption was also observed with lyophil-ized protein formulations containing polymer excipients such as dextran and polyvinyl alcohol.856 857

Was this article helpful?

0 0
Drug Addiction

Drug Addiction

If you're wanting to learn about drug addiction... Then this may be the most important letter you'll ever read You Are Going To Get A In Depth Look At One Of The Most Noteworthy Guides On Drug Addiction There Is Available On The Market Today. It Doesn't Matter If You Are Just For The First Time Looking For Answers On Drug Addiction, This Guide Will Get You On The Right Track.

Get My Free Ebook


Post a comment