Polymeric carrier-mediated intracellular delivery of phosphatidylinositol-3,4,5-trisphosphate to overcome insulin resistance

Background: Phosphatidylinositol-3,4,5-trisphosphate (PIP₃) is a major lipid second messenger in insulin-mediated signalling towards the metabolic actions of this hormone in muscle and fat.Purpose: Assessing the intracellular transport of exogenous PIP₃ attached to a polymeric carrier in an attempt to overcome cellular insulin resistance.Methods: Artificial chromatic bio-mimetic membrane vesicles composed of dimyristoylphosphatidylcholine and polydiacetylene were applied to screen the polymeric carriers. PIP₃ cellular localization and bio-activity was assessed by fluorescent and live-cell microscopy in L6 muscle cells and in 3T3-L1 adipocytes.Results and discussion: We demonstrate that a specific-branched polyethylenimine (PEI-25, 25 kDa) carrier forms complexes with PIP₃ that interact with the bio-mimetic membrane vesicles in a manner predictive of their interaction with cells: In L6 muscle cells, PEI-25/fluorescent-PIP₃ complexes are retarded at the cell perimeter. PEI-25/PIP₃ complexes retain their bio-activity, engaging signalling steps downstream of PIP₃, even in muscle cells rendered insulin resistant by exposure to high glucose/high insulin.Conclusions: Inducing insulin actions by intracellular PIP₃ delivery (PEI-25/PIP₃ complexes) in some forms of insulin-resistant cells provides the first proof-of-principle for the potential therapeutic use of PIP₃ in a "second-messenger agonist" approach. In addition, utilization of an artificial bio-mimetic membrane platform to screen for highly efficient PIP₃ delivery predicts biological function in cells.