Parenteral Delivery of Peptides and Proteins - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 540

to form a stable protein delivery system because it will usually form the starting bulk
material before any other manipulations are undertaken, like lyophilization, emulsifi-
cation, or spray drying.
If a protein drug is to be transformed from a liquid to a powder by lyophiliza-
tion or spray drying during the formulation of the delivery system, more than one
additive may be required to stabilize the protein. The different chemical ingredients
used to stabilize protein formulations during development and their mechanisms are
discussed later.
11.3.1 Serum Albumin
Among proteinic additives, albumins and gelatins are those mainly used for protection
purposes. The protective effect of albumins against protein unfolding and aggregation
has been extensively documented and is likely due to their surface-active properties.
Albumins (i.e., bovine, human, or rat serum albumins) are thought to occupy the inter-
faces and shield the therapeutic proteins from contact with the solvents or hydrophobic
surfaces. Significant protein protection has been achieved after the addition of serum
albumin to the inner aqueous phase during the primary emulsification step of multiple
emulsion procedures. Thus, in one study, BSA was able to preserve more than 80%
of IGF-I integrity upon water-oil emulsification and ultrasonication [98] . Albumins
increased TT immunoreactivity from 8% to 82%, contrasting with ovalbumin (OVA),
which showed twofold less effectivity [87] . BSA improved the carbonic anhydrase
release profile probably by reducing protein aggregation and thereby minimizing non-
specific protein adsorption onto the polymer surface [86] . BSA is also thought to scav-
enge protons during polymer degradation, thereby avoiding any aggregation resulting
from acidity [99] . Examples of commercial protein solution formulations containing
albumin are alglucerase (1.0% human serum albumin (HSA), EPO (0.25% HSA),
interferon -2a (0.5% HSA), interferon -2b (0.1% HSA), and urokinase (5.0%
HSA). However, in all these formulations, albumin was not observed to be the univer-
sal stabilizer. For instance, albumin did not reduce the loss of trypsin and NGF activity
during the double emulsion process [100,101] .
The other proteinic additive used is gelatin, which is composed of a heteroge-
neous mixture of water-soluble proteins. The protective effect is dependent on the
gelatin's molecular weight and concentration. It has been obsereved that the higher
the molecular weight/concentration, the better the stabilization effect [85] . Gelatin
was also found to improve the antigenicity of tetanus toxoid during release [91] , and
succinylated gelatin significantly protected IGF-I against ultrasonication, preserving
up to 90% of its integrity. When gelatin was associated with BSA, IGF-I integrity
was fully preserved [98] . Although albumins and gelatin may stabilize the protein
formulations, these agents may complicate all subsequent protein characterization
within the formulation, thus hindering their use during formulation development.
11.3.2 Amino Acids
Certain amino acids may sometimes also act as stabilizers; however, they have been
used rarely. EPO aggregation was significantly reduced by L-arginine, probably by