Biodegradable laminar implants for sustained release of recombinant human growth hormone

Silica-collagen nanoformulations with extended human growth hormone release

Growth hormone deficiency has been treated by the daily administration of recombinant human growth hormone (hGH) for decades. Patient compliance to this treatment is generally incomplete due to challenges including dose frequency and lack of perceived benefits. This stimulates the research on new formulations to reduce the number of periodic administrations. In this study silica nanoparticles and silica-collagen nanocomposites were evaluated for hGH loading and release. Bare nanoparticles showed higher hGH adsorption capacity than thiol- and isobutyl-bearing particles of similar diameters. Monitoring of bound protein conformation changes indicated hGH structure retention when adsorbed on bare silica nanoparticles and suggested no alterations on protein activity. Protein-loaded particles incorporated into collagen matrices (silica-collagen nanocomposites) showed a progressive protein release profile different from the observed for hGH-loaded silica nanoparticles and hGH-loaded collagen matrices. While both the collagen and the silica nanoparticle systems reached a 100 % release after 4 and 7 days respectively, silica-collagen nanocomposites showed a bi-phasic prolonged hGH release reaching approximately an 80 % after 15 days. These findings suggest that biocompatible silica-collagen nanocomposites could be used as vehicles for the prolonged delivery of hGH which could lead to a potential reduction in the number of periodic administrations.

Design and synthesis of polyacrylic acid/deoxycholic acid-modified chitosan copolymer and a close inspection of human growth hormone-copolymer interactions: An experimental and computational study

Despite efforts to achieve a long-acting formulation for human growth hormone (hGH), daily injections are still prescribed for children with growth hormone deficiency. To grapple with the issue, acquiring a deep knowledge of the protein and understanding its interaction mechanism with the carrier can be beneficial. Herein, we designed and synthesized a novel chitosan-based copolymer and investigated its interaction with hGH using a combination of experimental and computational strategies. To construct the amphiphilic triblock copolymers (CDP), we grafted deoxycholic acid (DCA) and polyacrylic acid (PAA) onto the chitosan chains, and Fourier-transform infrared (FTIR) analysis confirmed the proper formation of CDP. Circular dichroism (CD) demonstrated the preservation of the secondary structure of hGH interacting with CDP, and, further, fluorescence spectroscopy proved the stability of the tertiary structure of the protein. Applying molecular dynamics simulation (MD), we examined the dynamics and integrity of hGH in the presence of the copolymer and compared its behavior with the protein in aquatic environments. Additionally, energy and contact analysis illustrated that the residues involved in the interaction were located predominantly in the connecting loops, and van der Waals (vdW) and electrostatic interactions were the main driving forces of the polymer-protein complex formation. This research's main aim was to trace the protein-polymer interaction's mechanism. We anticipate that the utility of the copolymer can address the challenges of fabricating a new sustained-release delivery platform for therapeutic proteins.

Long-Lasting Growth Hormone Regulated by the Ubiquitin-Proteasome System

To increase the half-life of growth hormones, we proposed its long-lasting regulation through the ubiquitin-proteasome system (UPS). We identified lysine residues (K67, K141, and K166) that are involved in the ubiquitination of human growth hormone (hGH) using ubiquitination site prediction programs to validate the ubiquitination sites, and then substituted these lysine residues with arginine residues. We identified the most effective substituent (K141R) to prevent ubiquitination and named it AUT-hGH. hGH was expressed and purified in the form of hGH-His, and ubiquitination was first verified at sites containing K141 in the blood stream. Through the study, we propose that AUT-hGH with an increased half-life could be used as a long-lasting hGH in the blood stream.

mPEG-PLA and PLA-PEG-PLA nanoparticles as new carriers for delivery of recombinant human Growth Hormone (rhGH)

mPEG-PLA and PLA-PEG-PLA copolymeric nanoparticles with three different PLA to PEG ratios are synthesized and used for encapsulation of recombinant human Growth hormone (rhGH). The structure and composition of the synthesized copolymers were analyzed by ¹H NMR and GPC techniques. Moreover, morphology, encapsulation efficiency (EE), cytotoxicity, release profile and stability of the encapsulated rhGH were measured. Structural analysis of the prepared copolymers showed that they were successfully synthesized with approximately expected molecular weight and relatively low size distribution. It was also revealed that by increasing amounts of PLA/PEG ratio, EE content and size of nanoparticles were increased. Release profile evaluation of rhGH from both formulations indicated that copolymeric nanoparticles of Di-B2 and Tri-B2 exhibited the best results among the synthesized nanospheres, by having initial burst release of 17.5% and 28% and then slow and constant release of rhGH up to 65% and 77% of the encapsulated drug, respectively. Furthermore, results of HPLC, SDS-PAGE and CD analyses showed stability of rhGH during encapsulation and release from nanoparticles. Finally, the results showed that these two formulations provided safe and efficient sustained release of rhGH for more than a month and they have the potential to do further studies under in vivo conditions.

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.

Controlled release of human growth hormone fused with a human hybrid Fc fragment through a nanoporous polymer membrane

Nanotechnology has been applied to the development of more effective and compatible drug delivery systems for therapeutic proteins. Human growth hormone (hGH) was fused with a hybrid Fc fragment containing partial Fc domains of human IgD and IgG4 to produce a long-acting fusion protein. The fusion protein, hGH-hyFc, resulted in the increase of the hydrodynamic diameter (ca. 11 nm) compared with the diameter (ca. 5 nm) of the recombinant hGH. A diblock copolymer membrane with nanopores (average diameter of 14.3 nm) exhibited a constant release rate of hGH-hyFc. The hGH-hyFc protein released in a controlled manner for one month was found to trigger the phosphorylation of Janus kinase 2 (JAK2) in human B lymphocyte and to exhibit an almost identical circular dichroism spectrum to that of the original hGH-hyFc, suggesting that the released fusion protein should maintain the functional and structural integrity of hGH. Thus, the nanoporous release device could be a potential delivery system for the long-term controlled release of therapeutic proteins fused with the hybrid Fc fragment.

A linear mixed-effects statistical model for in-vivo evaluation of recombinant human growth hormone implants in hypophysectomized rats

We have used a linear mixed-effects statistical model to evaluate previously published results of body weight evolution in hypophysectomized (Hpx) rats after administration of two different controlled-release formulations of recombinant human growth hormone (rhGH). Using the linear mixed-effects model, it was possible to distinguish between maximal pharmacological response with time in different subjects and relate it to the structure of the different formulations, the release of the hormone from them and the time necessary to obtain a quantitative result as a consequence of the hormone activity, contrary to the multivariate variance analysis model (MANOVA) used in our earlier work. These results confirmed that the maximum body weight gain obtained with the controlled-release implants is similar to that with subcutaneous rhGH, but with the advantage that laminar biodegradable implants need to be administered only once every 2 weeks.

A mathematical model for interpreting in vitro rhGH release from laminar implants

Recombinant human growth hormone (rhGH), used mainly for the treatment of growth hormone deficiency in children, requires daily subcutaneous injections. The use of controlled release formulations with appropriate rhGH release kinetics reduces the frequency of medication, improving patient compliance and quality of life. Biodegradable implants are a valid alternative, offering the feasibility of a regular release rate after administering a single dose, though it exists the slight disadvantage of a very minor surgical operation. Three laminar implant formulations (F(1), F(2) and F(3)) were produced by different manufacture procedures using solvent-casting techniques with the same copoly(D,L-lactic) glycolic acid (PLGA) polymer (Mw=48 kDa). A correlation in vitro between polymer matrix degradation and drug release rate from these formulations was found and a mathematical model was developed to interpret this. This model was applied to each formulation. The obtained results where explained in terms of manufacture parameters with the aim of elucidate whether drug release only occurs by diffusion or erosion, or by a combination of both mechanisms. Controlling the manufacture method and the resultant changes in polymer structure facilitates a suitable rhGH release profile for different rhGH deficiency treatments.

Stabilization of somatropin by heparin

Somatropin, human growth hormone (hGH), is an unstable protein, posing challenging problems for its formulation and long-term stability. Since hGH formed insoluble adducts with heparin our aim was to evaluate heparin as a stabilizing agent for the drug. These adducts were characterized by particle diameter, tertiary structure variations and release studies. Studies were also carried out to determine the stability of hGH in the presence and absence of heparin by an interfacial denaturation method and real-time stability studies by measuring hGH activity and particle diameter. Moreover, biological activity of hGH and hGH/UH (unfractionated heparin) adducts was identified by daily subcutaneous injections to hypophysectomized rats. There was a decrease in mean hydrodynamic particle diameter of hGH/UH adducts with increased pH (54.4 to 12.2 nm from pH 3 to pH 7) indicating that the adducts were either dissociating or dissolving at high pH. Furthermore, second-derivative spectroscopy indicated that complexation of hGH with heparin did not cause a major disruption in the tertiary structure of hGH but decreased the hydrophilic environment around the tyrosine residues. Release of hGH from hGH/UH adducts was pH and ionic strength dependent with the highest release at pH 8 (93%) and lowest release at pH 3 (0%) over the first hour. Interfacial denaturation methods indicated that vortex agitation over 120 s resulted in no change in the optical density of hGH/UH adducts compared with a substantial increase for hGH alone at pH 6.8. Real-time stability studies over 93 days demonstrated that hGH/UH adducts at both pH 3 and 7 with an excess of heparin produced the highest percent of active hGH remaining in the solution at 4 degrees C and 37 degrees C. The higher stability of hGH/UH adducts with excess heparin compared with the stoichiometric ratio was also confirmed by particle size measurements during storage. The biological activity of these adducts was comparable with hGH alone by weight-gain studies in hypophysectomized rats. The findings suggest the value of using hGH/heparin adducts to stabilize the protein.

Exogenous recombinant human growth hormone effects during suboptimal energy and zinc intake

Background

Energy and Zinc (Zn) deficiencies have been associated with nutritional related growth retardation as well as growth hormone (GH) resistance. In this study, the relationship between suboptimal energy and/or Zn intake and growth in rats and their response to immunoreactive exogenous recombinant human GH (GHi), was determined.

Results

Rats treated with GHi and fed ad-libitum energy and Zn (100/100) had increased IGFBP-3 (p < 0.05) as compared with NSS (215 ± 23 vs. 185 ± 17 ng/ml) along with similar body weight gain. Rats treated with GHi and fed suboptimal energy and full Zn (70/100) had significantly increased weight gain (109.0 ± 18.2 vs. 73.8 ± 11.0 g) and serum IGF-I levels (568 ± 90 vs. 420 ± 85 ng/ml), along with decreased total body water (TBW; 61.0 ± 1.6 vs. 65.7 ± 2.1%) as compared to NSS controls. However, body weight gain was reduced (p < 0.05) as compared with rats fed ad-libitum energy. Growth hormone treated rats fed only suboptimal Zn (100/70), had increased weight gain (217.5 ± 13.2 vs. 191.6 ± 17.9 g; p < 0.05) compared to those given NSS. These rats gained weight in similar amounts to those fed full Zn. Rats treated with GHi and fed both suboptimal energy and Zn (70/70) showed similar results to those fed suboptimal energy with appropriate Zn (70/100), along with significant increases in IGFBP-3 levels (322 ± 28 vs. 93 ± 28 ng/ml). All restricted rats had reduced 24-h EE (kcal/100 g BW) and physical activity index (oscillations/min/kg BW) and GHi did not overcome these effects.

Conclusion

These results suggest that GHi enhances weight gain in rats with suboptimal energy and Zn intake but does not modify energy expenditure or physical activity index. Suboptimal Zn intake did not exacerbate the reduced growth or decrease in energy expenditure observed with energy restriction.

Development of implant tablet for a week-long sustained release

An implant tablet for a week-long sustained release was developed by the direct compression method using poly-DL-lactic acid (PLA) and poly(DL-lactic acid-co-glycolic acid) copolymer (PLGA) as a matrix and phenol red (PR) as a model drug. The in vitro release was affected by formulations, especially by drug content and polymer species. The release rate correlated with the rate of absorption of water. The implant tablet (30 mg) containing 1 mg of PR, prepared using PLGA (MW 10,000; lactic acid/glycolic acid=1:1, mol/mol) by compression at 50 kg/cm(2) for 10 s, was found to efficiently exhibit a week-long sustained release in vitro, and applied in vivo. The remaining amount or plasma concentration of PR after s.c. administration of the implant tablet to rats demonstrated that the implant tablet showed a week-long sustained release in vivo. The present implant tablet is suggested to be useful as a drug delivery system for supplying drugs for approximately 1 week.