Sustained delivery of growth hormone from poly(e-caprolactone) diol/poly(ethylene glycol) injectable implants

GONZALEZ L.; CHIAPPETTA D.A.; TURYN D.; SOSNIK A.

Rosario

Taller; 1er Taller de Órganos Artificiales, Biomateriales e Ingeniería de Tejidos (BIOOMAT 2009); 2009

Centro Binacional (Argentina – Italia) de Criobiología Clínica y Aplicada (CAIC), Facultad de Ciencias Bioquímicas y Farmacéuticas de la Universidad Nacional de Rosario y Sociedad Latinoamericana de Biomateriales, Ingeniería de Tejidos y Órganos Artificia

Growth hormone (GH) therapy was developed in the early 1950s and was used successfully to treat growth hormone deficiency (GHD) in hypopituitary dwarfism. When recombinant DNA (rDNA) technology allowed the production of recombinant human GH (rhGH), the clinical indication was extended to several pathological conditions including pediatric GHD, adult GHD, chronic renal insufficiency, Turner´s syndrome and cachexia secondary to AIDS. Treatment is by frequent, usually daily or every other day, injections. The main disadvantages of current rhGH therapy is the short half-life of the hormone, its renal toxicity and the necessity of multiple injections; thus the rhGH is ideally intended for depot formulation producing continuous release of GH. However human growth hormone is a pituitary hormone normally secreted in a pulsatil pattern. With the aim of better understanding the benefits and drawbacks of both GH administration regimens (frequent injections vs. continuous release) we developed an injectable implant for the sustained released of GH in mice. To improve the aqueous solubility and its dispersability in the polymeric implant, the hormone was solubilized in PEG solutions containing different GH:PEG weight ratios, freeze-dried and lyophilized. Then, different GH amounts were dispersed in solutions of poly(ε-caprolactone) diol (~MW 5000 Da) in N-methyl pyrrolidone. The polymer was synthesized by the ring opening polymerization reaction of ε-caprolactone initiated by low molecular weight poly(ethylene glycol) (MW 400 Da, PEG400) and using stannous octanoate as the catalyst. The in vitro release kinetics was assayed. GH-containing samples (200 µL) were inoculated in individual vials containing 1.5 ml of isotonic phosphate buffer at pH 7.4 and incubated at 37ºC. The released medium was periodically removed and replaced by equal volumes of fresh buffer. GH concentration in the released medium was analyzed by the Bicinchronic Acid protein assay (BCA). Released GH was also analyzed by protein electrophoresis. Also, the developed GH-loaded injectable implant and the process maintained the GH structurally intact. Finally, the GH release profiles in vitro towards the in vivo studies were optimized by including different amounts of poly(ethylene glycol) (MW 3350, PEG3350). The incorporation of this highly hydrophilic component to the implant mixture led to a faster diffusion and more efficient release of the hormone.