Epithelial transport and bioavailability of intranasally administered human growth hormone formulated with the absorption enhancers didecanoyl-L-alpha-phosphatidylcholine and alpha-cyclodextrin in rabbits

Developments in human growth hormone preparations: sustained-release, prolonged half-life, novel injection devices, and alternative delivery routes

Since the availability of recombinant human growth hormone (rhGH) enabled the application of human growth hormone both in clinical and research use in the 1980s, millions of patients were prescribed a daily injection of rhGH, but noncompliance rates were high. To address the problem of noncompliance, numerous studies have been carried out, involving: sustained-release preparations, prolonged half-life derivatives, new injectors that cause less pain, and other noninvasive delivery methods such as intranasal, pulmonary and transdermal deliveries. Some accomplishments have been made and launched already, such as the Nutropin Depot^® microsphere and injectors (Zomajet^®, Serojet^®, and NordiFlex^®). Here, we provide a review of the different technologies and illustrate the key points of these studies to achieve an improved rhGH product.

Reestablishment of the nasal permeability barrier to several peptides following exposure to the absorption enhancer tetradecyl-beta-D-maltoside

Regular insulin, NPH insulin, glargine insulin, calcitonin, and human growth hormone were administered to rats nasally with 0.125% tetradecyl-beta-D-maltoside (TDM), or at various times after TDM treatment. Absorption of all five peptides was enhanced initially and diminished in a time-dependent manner as the interval between administration of TDM and the peptide increased. Changes in nasal morphology were also assessed via transmission electron microscopy (TEM) immediately after TDM treatment and at various times thereafter. TEM analysis demonstrated that 0.125% TDM caused a rapid and transient alteration in the morphology of the apical membrane surface. Fewer cilia were observed and cell-cell junctions were difficult to visualize, but no epithelial cell erosion was apparent. Two hours after TDM treatment, the apical membrane surface once again contained abundant cilia and cell-cell junctions were readily visualized. The complete recovery of the nasal permeability barrier to several different peptides following TDM administration and the concomitant histological evidence demonstrate that TDM treatment transiently perturbs the nasal mucosa to stimulate peptide drug absorption and does not produce irreversible damage to the cells that line the nasal cavity.

Nasal delivery of high molecular weight drugs

Nasal drug delivery may be used for either local or systemic effects. Low molecular weight drugs with are rapidly absorbed through nasal mucosa. The main reasons for this are the high permeability, fairly wide absorption area, porous and thin endothelial basement membrane of the nasal epithelium. Despite the many advantages of the nasal route, limitations such as the high molecular weight (HMW) of drugs may impede drug absorption through the nasal mucosa. Recent studies have focused particularly on the nasal application of HMW therapeutic agents such as peptide-protein drugs and vaccines intended for systemic effects. Due to their hydrophilic structure, the nasal bioavailability of peptide and protein drugs is normally less than 1%. Besides their weak mucosal membrane permeability and enzymatic degradation in nasal mucosa, these drugs are rapidly cleared from the nasal cavity after administration because of mucociliary clearance. There are many approaches for increasing the residence time of drug formulations in the nasal cavity resulting in enhanced drug absorption. In this review article, nasal route and transport mechanisms across the nasal mucosa will be briefly presented. In the second part, current studies regarding the nasal application of macromolecular drugs and vaccines with nano- and micro-particulate carrier systems will be summarised.

Intranasal delivery of recombinant human growth hormone (somatropin) in sheep using chitosan-based powder formulations

The effectiveness of chitosan in promoting the intranasal bioavailability of recombinant human growth hormone (hGH) has been evaluated. hGH was formulated with chitosan to produce a powder blend (Formulation A) and granules (Formulation B) for intranasal administration. The in vivo pharmacokinetic performance of the formulations was evaluated in a group of six sheep in a randomised crossover study. A subcutaneous injection of hGH solution was administered as a control. The intranasal and subcutaneous doses of hGH were 0.3 and 0.03 mg/kg, respectively. The intranasal formulations appeared to be well tolerated. Mean bioavailabilities of hGH from Formulations A and B were 14 and 15%, respectively relative to subcutaneous injection. It is concluded that chitosan-based intranasal powder formulations may provide a practical means for non-injectable delivery of hGH and, potentially, other therapeutic protein molecules.

Correlation of tetradecylmaltoside induced increases in nasal peptide drug delivery with morphological changes in nasal epithelial cells

The effect of tetradecylmaltoside (TDM) on nasal peptide drug absorption was assessed with four peptides of distinct molecular size: insulin (5.7 kDa), leptin (16 kDa), somatropin (22.1 kDa), and epoetin alfa (30.4 kDa). The nasal uptake of the smallest peptides, insulin and leptin, was significantly increased at a TDM concentration of only 0.06%. The uptake of somatropin was significantly increased when concentrations of 0.125% or more were used. The uptake of the largest peptide, epoetin alfa, was not significantly increased, in the presence of 0.125-0.5% TDM. Light microscopy revealed that formulations containing 0.125% TDM caused moderate alterations in nasal epithelial cell morphology, while higher concentrations of TDM (0.5%), caused more extensive morphological changes. Following treatment with 0.125% TDM, the distribution of cilia was altered and the number of pinocytotic vesicles was increased, at a time that correlated with increased nasal absorption of insulin. Consistent with these findings, FITC-insulin applied nasally in the absence of TDM did not enter nasal epithelial cells, whereas FITC-insulin co-administered with 0.125% TDM was internalized into the cells, with a uniform distribution, consistent with transcellular movement of the peptide through the cells.

Thiomers in noninvasive polypeptide delivery: in vitro and in vivo characterization of a polycarbophil-cysteine/glutathione gel formulation for human growth hormone

This study was aimed at investigating the potential of a new polycarbophil-cysteine (PCP-Cys)/glutathione (GSH) gel formulation to enhance the permeation of the model drug human growth hormone (hGH) across nasal mucosa in vitro and in vivo. The aqueous nasal gel contained PCP-Cys, GSH, and hGH in a final concentration of 0.3%, 0.5%, and 0.6% (m/v), respectively. In vitro permeation studies were performed in Ussing chambers on freshly excised bovine nasal mucosa using fluorescence-labeled dextran (molecular mass: 4.3 kDa; FD-4) and hGH (FITC-hGH). The release profile of FITC-hGH from the gel formulation and an unmodified PCP control formulation was determined. Furthermore, in vivo studies in rats were performed comparing the PCP-Cys/GSH/hGH gel with PCP/hGH control gel and physiological saline. The permeation of FD-4 and FITC-hGH across the nasal mucosa was improved two-fold and three-fold, respectively, in the presence of PCP-Cys/GSH. The PCP-Cys/GSH/hGH gel and the PCP/hGH control gel showed the same biphasic and matrix-controlled drug release. The nasal administration of the PCP-Cys/GSH/hGH gel formulation to rats resulted in a significantly increased and prolonged hGH plasma concentration-time profile versus unmodified PCP gel and physiological saline. According to these results, PCP-Cys gels might represent a promising new strategy for systemic nasal polypeptide delivery.

Pharmacokinetic evaluation of ipamorelin and other peptidyl growth hormone secretagogues with emphasis on nasal absorption

1. The pharmacokinetics of three new peptidyl growth hormone secretagogues, ipamorelin (NNC 26-0161), NNC 26-0194 and NNC 26-0235, were compared with two well-known hexapeptides, GHRP-2 and GHRP-6, in the male rat following different routes of administration. 2. Following i.v. bolus injection, plasma concentrations of the peptides declined biexponentially. Ipamorelin differed markedly from the other peptides investigated, demonstrating a systemic plasma clearance 5-fold lower than that of GHRP-6. Ipamorelin was mainly excreted in the urine, whereas GHRP-6 was predominantly excreted in the bile. NNC 26-0194 and NNC 26-0235 also showed high biliary excretions. Ipamorelin and the two NNC peptides were moderately resistant towards metabolism as 60-80% of the administered dose could be recovered from bile and urine as intact peptide. 3. After intranasal application, the bioavailability of ipamorelin was estimated at approximately 20%. Higher bioavailabilities of approximately 50% were determined for NNC 26-0235, NNC 26-0194 and GHRP-2, whereas the nasal absorption of GHRP-6 was somewhat lower. Thus, the peptides could be easily transported across the nasal epithelium suggesting that the nasal route seems promising for systemic delivery of this family of peptidyl growth hormone secretagogues.

Peptide hormones: Review of current and emerging uses by nasal delivery

The family of clinically available peptide hormones (PHs) is expanding in an exponential way, and advancement of knowledge of the basic mechanisms of action of PHs has led to multiplication of the possible clinical indications of already known PHs, and appears even more promising for still unknown PHs. A common obstacle to a full routine use of PHs is represented by the fact that PHs cannot be administered by the oral route, since they undergo digestion and inactivation in the gastrointestinal tract and a significant first pass metabolism in the liver. One alternative is represented by intranasal administration of PHs. The intranasal route of administration of PHs is also very attractive because of its convenience, which should assure a good compliance by patients. Luteinizing hormone releasing hormone, the analogues, desmopressin, oxytocin and salmon calcitonin are already marketed for intranasal administration; for salmon calcitonin, studies about bioavailability have been scanty in the past, but should be re-considered in order to fully explore its clinical benefit.Intranasal peptide hormones not yet on the market are insulin, glucagon, growth hormone releasing hormone (GHRH) and GHRP, GH and somatostatin, but the scenario is likely to change in a short period of time. Hexarelin seems very effective and is at a promising stage of development; also, glucagon appears mature enough to undergo extensive clinical evaluation and possibly marketing. The concern is why other peptides have not been further evaluated, as is the case for somatostatin and its analogues.

Pharmaceutical applications of cyclodextrins. III. Toxicological issues and safety evaluation

The objective of this review is to summarize recent findings on the safety profiles of three natural cyclodextrins (alpha-, beta- and gamma-CDs) and several chemically modified CDs. To demonstrate the potential of CDs in pharmaceutical formulations, their stability against non-enzymatic and enzymatic degradations in various body fluids and tissue homogenates and their pharmacokinetics via parenteral, oral, transmucosal, and dermal routes of administration are outlined. Furthermore, the bioadaptabilities of CDs, including in vitro cellular interactions and in vivo safety profiles, via a variety of administration routes are addressed. Finally, the therapeutic potentials of CDs are discussed on the basis of their ability to interact with various endogenous and exogenous lipophiles or, especially for sulfated CDs, their effects on cellular processes mediated by heparin binding growth factors.

Pharmaceutical applications of cyclodextrins. 2. In vivo drug delivery

The objective of this Review is to summarize and critique recent findings and applications of both unmodified and modified cyclodextrins for in vivo drug delivery. This review focuses on the use of cyclodextrins for parenteral, oral, ophthalmic, and nasal drug delivery. Other routes including dermal, rectal, and pulmonary delivery are also briefly addressed. This Review primarily focuses on newer findings concerning cyclodextrin derivatives which are likely to receive regulatory acceptance due to improved aqueous solubility and safety profiles as compared to the unmodified cyclodextrins. Many of the applications reviewed involve the use of hydroxypropyl-beta-cyclodextrins (HP-beta-CDs) and sulfobutylether-beta-cyclodextrins (SBE-beta-CDs) which show promise of greater safety while maintaining the ability to form inclusion complexes. The advantages and limitations of HP-beta-CD, SBE-beta-CD, and other cyclodextrins are addressed.