Release of adenosine from chitosan beads

摘要

Introduction: As many as 27 million American suffer from the painful chronic condition of osteoarthritis. Most treatments are geared toward symptom management, but recent advancements in tissue engineering aim to heal articular cartilage. Recent literature has shown that adenosine reduces inflammation, increases proliferation and matrix production, and promotes chondrocyte growth in osteoarthritic models. This study was conducted to demonstrate efficacy of chitosan microbeads as a delivery vehicle for adenosine. Methods: Chitosan (Chitopharm S) solutions (2% w/v) were created by dissolving 3 or 6 mg/mL adenosine base powder (MP Biomedicals) in 2% acetic acid, adding chitosan and stirring overnight. An emulsion was created by stirring the solution with an impeller at a setting of 2000 rpm in a 1:1 mixture of light to heavy chain mineral oil and 1 % Span 80. Glyoxal was added at 0.5% to the emulsion and the mixture was heated at 70°C while impelling for 24 hours. Microbeads were recovered by centrifugation and washing with hexanes, methanol, and then acetone. Four separate samples of dried beads weighing 50 mg were added to 1 mL sterile DMEM/High-glucose and vortexed. Eluate samples were taken every day for 7 days after vortexing and centrifugation. Adenosine concentration was measured with high performance liquid chromatography and normalized to known standard concentrations. Results: Higher concentrations of adenosine were observed in the elution samples collected over the first two days of the trial, with a peak elution of 1360 μg/ml on day two of elution for 6mg/ml concentration (Figure 1). The presence of adenosine in elution samples declined constantly over the next five days in a first-order release pattern for both loading concentrations. Discussion: Injectable chitosan microbeads deliver controlled amounts of adenosine over time, which offers advantages for drug delivery systems directed toward cartilage repair. By altering adenosine concentration in microbeads, elution profile and duration of the drug release can be controlled. Since previous studies have shown highest bioactivity of adenosine in the range of 50-200 μg/ml, loading with the lower amount may have improved therapeutic effect over the high-dose loaded microbeads. Evaluation of adherence of adenosine-loaded microbeads to damaged tissue as well as testing efficacy in promoting cell growth through in vitro chondrocyte cell culture and preclinical models will provide insight into the refinement of functional delivery systems. Conclusions: Adenosine-loaded microbeads may provide effective controlled delivery of bioactive adenosine for applications in promoting healing of cartilage, skin, bone, and soft tissues. Minimally invasive delivery, inexpensive cost, and biocompatibility may offer an advantage of adenosine-loaded chitosan microbeads over other treatment options for tissue repair, such as surgical procedures, joint replacement, and growth factor therapy.