Peptides, nasal formulations

Several peptide products used in the treatment of diabetes mellitus, in addition to insulin, are currently administered by subcutaneous injection and these drugs are candidates for development of nasal formulations. Glucagon-like peptide-1 (GLP-l)-related peptides stimulate the insulin response to glucose and diminish the release of glucagon after a meal. These effects diminish the excessive postprandial increase in glucose observed after a meal in persons with type 2 diabetes mellitus. GLP-1-related peptides must be administered by subcutaneous injection before meals in order to be effective. This requirement for injection before each meal is likely to impact the utilization of these products by persons with type 2 diabetes. Exendin-4 is a GLP-1-related peptide with a molecular mass of 4.2 kDa. The development of a GLP-1-related peptide nasal formulation containing an absorption enhancer would allow patients to scll-administer one of these drugs just before a meal without the need for a subcutaneous injection. 

Chitosan is a cationic polysaccharide produced from the deacetylation of chitin, a component of crab and shrimp shells [7,57,58], Chitin is composed of units of 2-deoxy-2-(acetylamino) glucose joined by glycosidic bonds that form a linear polymer. Ilium et al. [7,57,58] demonstrated the ability of chitosan to increase the bioavailability of insulin and other small peptides and polar macromolecules in different animal models. In both the sheep and rat models, the addition of chitosan at concentrations of 0.2%-0.5% to nasal formulations of insulin resulted in significant increases in plasma insulin and reductions in blood glucose. Reversibility studies indicated that the effect of chitosan on the nasal absorption of insulin... 

Calcitonin is a peptide hormone produced in the thyroid gland that serves to lower serum calcium and phosphate levels by inhibiting bone resorption. Calcitonin has been used in the treatment of a variety of diseases, such as primary hyperparathyroidism, Paget s disease, and postmenopausal osteoporosis [99,100]. Salmon calcitonin has a longer half-life than human calcitonin. Salmon calcitonin, 3.6 kDa, is available as a nasal formulation that contains only benzalkonium chloride as a preservative, without an absorption enhancer, and as a parenteral product for injection. The direct effect of benzalkonium chloride on the nasal mucosa is under... 

Leptin is a peptide hormone secreted by adipocytes. Recombinant human leptin has been investigated for its potential as an antiobesity agent [105,106]. Women with hypothalamic amenorrhea display reduced levels of leptin. Leptin administration to these women improves reproductive and neuroendocrine function [107], Nasal administration of leptin to rats in the presence of either TDM (1) or LPC [108] caused a significant increase in serum leptin levels. Increased serum leptin levels were associated with reduced food consumption [108], The development of an effective nasal formulation of leptin containing an absorption enhancer may allow more frequent dosing with leptin and thereby overcome the limited efficacy observed following subcutaneous injections of large doses of this hormone. 

The administration of systemically acting products via the nasal route began in the 1980s. The peptide oxytocin, which stimulates uterine contraction and lactation, was one of the first nasally administered peptide hormones. Meanwhile, several peptide-based nasal formulations entered the market. Currently, more attention is being paid to this delivery system due to the increasing demands of new highly potent drug formulations. In addition, patients expectations for... 

Table 1 Marketed products and pipeline of nasal peptide/protein formulation...

Penetration enhancers are often used to improve peptide bioavailability in nasal formulations. A variety of different enhancers have been tried, and they work by one or several combined mechanisms. Some act by increasing the membrane fluidity and reducing the viscosity of the mucus layer, thereby increasing membrane permeability. Others act by transient loosening of the tight junctions between epithelial cells. The types of penetration enhancers discussed in the research literature include the following. 

In 1992, Drejer et al. [31] investigated the pharmacokinetics of intranasal insulin containing a medium-chain phospholipid (didecanoyl-L-alpha-phosphatidylcho-line) as absorption enhancer in 11 normal volunteers. Intranasal insulin was absorbed in a dose-dependent manner with a mean plasma insulin peak 23 7 min after administration. Mean plasma glucose nadir was seen after 44 6min, 20min after intravenous injection. Moreover, intranasal administration of insulin resulted in a faster time-course of absorption than subcutaneous injection, and the bioavailability for the nasal formulation was 8.3% relative to an intravenous bolus injection when plasma insulin was corrected for endogenous insulin production estimated by C-peptide. 

The nasal tissue is highly vascularized and provides efficient systemic absorption. Compared with oral or subcutaneous administration, nasal administration enhances bioavailability and improves safety and efficacy. Chitosan enhances the absorption of proteins and peptide drugs across nasal and intestinal epithelia. Gogev et al. demonstrated that the soluble formulation of glycol chitosan has potential usefulness as an intranasal adjuvant for recombinant viral vector vaccines in cattle [276]. 

Ilium, L., Bioadhesive Formulations for Nasal Peptide Delivery. In Bioadhesive Drug Delivery Systems (E. Mathiowitz, D.E. Chiekering, III, and C.-M. Lehr, eds.), Marcel Dekker, Inc., New York, 1999, pp. 507-539. 

A host of bioadhesive controlled release systems have been proposed in recent years. Among the most commonly studied applications of bioadhesive materials is the area of buccal controlled delivery [408], The buccal delivery of small peptides from bioadhesive polymers was studied by Bodde and coworkers [409], and a wide range of compositions based on poly(butyl acrylate) and/or poly(acrylic acid) gave satisfactory performance. Bioadhesive poly(acrylic add)-based formulations have also been used for oral applications [402,410] for the sustained delivery of chlorothiazide [410] and for a thin bioadhesive patch for treatment of gingivitis and periodontal disease [411]. Other bioadhesive applications of polyelectrolytes include materials for ophthalmic vehicles [412,413], and systems for oral [410,414,415-419], rectal [420,421] vaginal [422] and nasal [423] drug delivery. 

The mucus layer also bathes the cilia of ciliated epithelial surface cells and provides a stimulus for ciliary motility (i.e., ciliary beating). The cilia consist of microtubules with a 9 + 2 configuration (nine pairs of peripheral microtubules and two central microtubules) that beat rhythmically to rapidly move mucus from the anterior to the posterior portion of the nasal cavity. To successfully cross the nasal permeability barrier, peptide drugs must penetrate the mucus layer and cross the epithelial cell layer, and do so in a limited time, because mucociliary clearance will limit the time of exposure of the peptide to the absorptive surface [19-21,27-29], Typically, drugs or inspired particles that are delivered nasally are removed via mucociliary clearance, with a clearance time of approximately 15 min in humans however, this transit time can vary from person to person and can be impacted by the addition of mucoadhesive agents to the formulation [30-37],... 

Since its discovery, isolation, and purification in the early twentieth century, insulin has been administered to diabetic patients exclusively by injection until the recent introduction of inhaled insulin. Insulin possesses certain physiochemical properties that contribute to its limited absorption from the gastrointestinal tract, and requires subcutaneous injection to achieve clinically relevant bioavailability. With a molecular size of 5.7 kDa, insulin is a moderately sized polypeptide composed of two distinct peptide chains designated the A chain (21 amino acid residues) and the B chain (30 amino acid residues) and joined by two disulfide bonds. Like all polypeptides, insulin is a charged molecule that cannot easily penetrate the phospholipid membrane of the epithelial cells that line the nasal cavity. Furthermore, insulin monomers self-associate into hexameric units with a molecular mass greater than 30 kDa, which can further limit its passive absorption. Despite these constraints, successful delivery of insulin via the nasal route has been reported in humans and animals when an absorption enhancer was added to the formulation. 

Since a comprehensive listing of every potential peptide and macromolecule that could be delivered nasally is not possible, this section will focus on (1) the drugs currently in use as nasal products in humans, (2) drugs currently in use as injectables in humans that will gain increased utilization if and when they can be formulated for nasal delivery, and (3) drugs that are currently in development for utilization in humans (Table 20.2). 

The introduction of safe, effective absorption-enhancing agents represents the critical element limiting the widespread use of nasal peptide formulations. Progress in this area has been slow to date, but several agents appear to have the potential to enable consistent and efficient absorption of peptide drugs from the nose. 

Nasal administration. Apart from parenteral administration, controlled release dosage forms based upon the microsphere concept should have application to other routes of administration. Microspheres in the form of pellets have been used to deliver drugs to the gastrointestinal tract and other examples include the administration of microspheres to the eye and topically to the lungs. In recent studies Ilium (20) has employed microspheres as possible controlled release formulations for nasal application. Such studies have relevance to the delivery of novel macromolecular compounds such as peptides and proteins. 

Additional factors influencing nasal peptide absorption include particle residence time and formulation pH and osmolarity. Ohwaki et al (10) measured the effect of solution pH and osmolarity on the intranasal absorption of secretin, a 27 amino acid peptide, in rats. Nasal secretin absorption, as measured by pancreatic secretion rates, was maximal at a formulation pH of 3.0 almost eight times greater than at neutral pH. Solution osmolarity had less effect overall on secretin absorption, maximal absorption occurring in a hyperosmolar saline solution of 0.462 M. 

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