Protein and Peptide Delivery through Respiratory Pathway - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 432

formulations must be prepared with an inert gas, for example, via nitrogen purging
during manufacturing, and must be stored in containers with inert gas on headspace.
9.3.4.2.5 Degradation Rate as a Function of pH
A minimum degradation rate of between pH 4 to 8 occurs. A number of peptide and
protein drugs have maximum stability between pH 5 to 7 [13] . The stability of pro-
tein and peptide drugs is well controlled by citrate and/or phosphate buffers in this
pH range.
9.3.5 Characterization of Peptide and Protein Drugs
A wide variety of analytical techniques based on the physical, chemical, and bio-
logical properties of peptide and protein drugs have been employed in the study of
their stability. Most of these methods require the step of separating the principle pro-
tein from microheterogeneous mixtures by quantization. Any method of analysis that
claims to indicate stability for protein drugs must be validated by bioassay.
9.3.5.1 Stability-Indicating Assays Based on Physical Properties
There are a number of physical measurements based on hydrodynamic properties,
such as intrinsic viscosity; sedimentation velocity or electrophoretic mobility; spectral
properties, such as fluorescence, ultraviolet, and visible light absorbance, or circular
dichroism; surface charge properties, like electrophoretic mobility; and adsorption/
affinity properties involved in liquid partition chromatography, gel permeation chro-
matography, microcalorimetry, and mass spectrometry.
9.3.5.2 Stability-Indicating Assays Based on Chemical Properties
Characterization of protein and peptide drugs involves determining the primary
sequence of amino acids and identifying prosthetic groups (fatty acids, carbohydrates,
etc.) that are covalently linked to the peptide backbone. Active site titration and kinetic
assays are chemical derivatization techniques that especially apply for the character-
ization of enzymes.
9.3.5.3 Stability-Indicating Assays Based on Biological Properties
Biological effects of proteins and peptides are assessed by whole-organism bioassay
and receptor-binding studies. Bioassays are generally stability indicating, and it is
always possible to perform a stability-indicating bioassay for a protein or peptide
drug. Receptor binding is measured in cells grown in culture. Alternatively, antibod-
ies to the peptide or protein drugs are raised, and the binding properties of the anti-
body for the drug can be correlated with whole-organism biological activity.
9.3.6 Absorption and Bioavailability of Inhaled Peptides and Proteins
Systemic delivery of peptides via the respiratory tract has become an important area
of research in the last decade, apparently as a result of high permeability of lung