Can myoglobin expression in pancreatic beta cells improve insulin secretion under hypoxia? An exploratory study with transgenic porcine islets.

The feasibility of myoglobin (Mb)-facilitated oxygen transport in improving porcine islet survival under hypoxia was investigated. Discrete groups of islets were transfected with replication-defective adenoviral vector Ad5 respiratory syncitial virus (RSV) to induce expression of Mb or green fluorescent protein (GFP). Native islets served as the controls. In vitro studies at 37 degrees C assessed islet insulin secretion efficacy: (i) to a glucose challenge from 30 to 300 mg/dL at fixed pO2; and (ii) at variable oxygen tensions ranging from 5 to 40 mm Hg over 12 h. The transfection was effective in initiating islet expression of Mb or GFP. Low Mb-expression levels equivalent to 2% the Mb concentration in a muscle cell (0.25 ng of Mb per islet) were documented, with no statistical improvement in insulin secretion. A surprising side note is that insulin secretion was impaired in islets expressing GFP. Improved Mb expression is essential to determine the feasibility of enhancing islet survival under hypoxia.