Proteomics - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 419

�.7.�.4.� Practical Aspects Associated with Silver Staining
To increase the efficacy of staining, prolonged exposure to the washing solution
is advisable. This treatment also reduces background noise levels. Development
of the gel for a very long time may result in a poor yield of peptides during mass
spectrometric analysis due to the elution of unstained peptides. The problem gets fur-
ther complicated because of the proteolytic action of trypsin.
In cases of excessive protein, negative staining is likely. In some cases, artificially
colored bands may be observed due to the presence of an excess of reducing agents
in the buffer. Hence, these are some of the practical issues that need to be considered
when using the silver staining technique.
8.8 Pharmacokinetics of Proteins
Delivery of proteins and peptides as drug candidates by oral route is a major chal-
lenge to pharmaceutical scientists. The high molecular weight, poor permeability
across gastric mucosa, size, acid lability, and susceptibility to proteolytic enzyme
action in the gut are some of the constraints of protein delivery. Proteins have been
found to undergo extensive premature metabolism in the gut due to proteases and
other proteolytic enzymes. All these hurdles in protein absorption render the oral
route as inappropriate, and it is the least preferred route for protein and peptide drug
delivery. Hence, parenteral routes like intravenous (i.v.), subcutaneous (s.c.), and so
on, are the principal preferred routes of drug delivery.
8.8.1 Injectable Routes for Protein Delivery
Administration of peptides and proteins by parenteral routes largely circumvents the
gastrointestinal tract and hence prevents premature metabolism prior to the systemic
absorption of proteins. This in turn improves protein concentration at the targeted
site. Logically, the intravenous route is the most preferred route of administration
in terms of time and the onset and duration of action. Many of the FDA-approved
protein products are administered by the i.v. route. However, at times it becomes
difficult to achieve optimum concentration of the protein, and accordingly, biologi-
cal activity is likely to vary. In such cases, Intramuscular (i.m.) and s.c. routes are
sometimes preferred over i.v. fusion or a bolus. Some studies report the superior-
ity of i.m. and s.c. route over the i.v. bolus or infusion. One of the studies shows
that s.c. administration of  erythropoetin has been found to successfully maintain
hematocrit levels in patients on hemodialysis as compared to the same administered
by i.v. route. However, major drawbacks of the i.m. and s.c. routes like degradation
of protein at the site of administration, injection-induced trauma, and fluctuations in
capillary size leading to erratic vascularization overshadow the usefulness of these
routes in protein delivery [48] . The s.c. administration of proteins and peptides is
followed by their systemic absorption via blood capillaries or lymphatics, depending
upon the size and molecular weight of the protein under consideration. It seems that