Introduction:
Therapeutic angiogenesis in Peripheral Arterial Disease (PAD) using stem cell therapy is potentially complicated by immunorejection. To overcome this problem, microen-capsulation using the alginate-poly-L-lysine (PLL)-alginate (APA) method was developed to provide a protective porous bubble to block antibodies but allow exchange of small molecules. Recently, we have developed a method to enable X-ray detection of these capsules. However, cell survival within the capsules could not be determined. Plus PLL can be mildly cytotoxic. In the present study, we combined reporter gene methods to verify cell survival with X-ray detection of the microcapsules in a rabbit PAD model and studied the PLL impact on cell viability.
Methods:
Rabbit mesenchymal stem cells (MSCs) were transfected with triple fusion (TF) reporter gene for bioluminescence (firefly luciferase), fluorescence (red fluorescent protein) and PET (truncated thymidine kinase). TF-MSCs were encapsulated in the perfluorooctyl bromide (PFOB) capsules to enable computed tomographic detection. Capsule crosslinking was performed with three PLL concentrations, i.e., 0.005%, 0.025% and 0.05%. Bioluminescent imaging (BLI) was used to monitor cells survival for one week
in vitro
and after intramuscular injection
in vivo
.
Results:
Serial
in vitro
BLI enabled the detection of viable encapsulated MSCs without detrimental signal degradation (~13% decrease of BLI signal intensity after PFOB encapsulation comparing to equal number of naked MSCs). PLL did not result in cell death; higher PLL concentrations were correlated with stronger BLI signal. BLI signal production was only slightly reduced by second layer of alginate (~80% for 0.05% PLL).
In vivo
BLI demonstrated the detection of naked, APA, and PFOB-encapsulated TF-MSCs. X-ray imaging enabled PFOB microcapsules detection relative to vasculature.
Conclusion:
BLI allows monitoring of encapsulated cells survival. PLL concentrations ≤ 0.05% appear safe for encapsulated cells with higher concentration being associated with enhanced crosslinking and capsule stability. MSCs expressing TF reporter in PFOB microcapsules enables dual monitoring of cell delivery/capsule tracking by X-ray imaging and cell viability with BLI.
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