In situ gene transfer into animal tendons by injection of naked DNA and electrotransfer

Abstract

Background: Degenerative or traumatic tendon injuries are extremely common but often heal poorly, not restoring the normal function of the injured tissues. Gene transfer could improve the repair process, by permitting local production of therapeutic substances, e.g. growth factors.

Methods and results: Injection of a plasmid carrying the lacZ marker gene was performed into the Achilles tendons of rat and mouse, and the patellar tendons of rabbit. At 48 h, transduced cells were found in the injected zones of the tendons but represented a minority of the tendon cells. A kinetics study in rats permitted observation of a gradual decrease with time in the beta-gal-expressing cell number; at day 42 no more gene expression was detected. Noteworthy, no inflammatory reaction was observed. We then investigated whether electrotransfer could improve gene transfer efficacy in rat tendon by delivering in situ electric pulses after DNA injection. Gene transfer was improved at best by approximately 50% under certain electrical conditions (200 V for 10 ms or 1200 V for 100 micro s). Finally, multiple injections of plasmid permitted an increase in the number of transduced cells by approximately 400%.

Conclusions: In situ injection of naked DNA into tendons is a very simple technique that permits delivery of genes with a duration of expression sufficient for clinical application aimed at modulating healing or restoration of a degenerative tendon. Despite a low transfer efficiency, this method should be compatible with clinical applications aimed at delivering therapeutic substances acting at low concentration.