1 School of Medicine, University of Zagreb, Department of Histology and Embryology, Šalata 3, 10000 Zagreb, Croatia
2 Current address: AO Research Institute Davos, Clavadelerstrasse 8, 7270 Davos, Switzerland
3 Institute of Oncology Ljubljana, Zaloška cesta 2, 1000 Ljubljana, Slovenia
4 Children's Hospital Zagreb, Department of Paediatric Orthopaedics, Ulica Vjekoslava Klaića 16, 10000 Zagreb, Croatia
5 Ludwig Boltzmann Institute for Traumatology, The Research Center in Cooperation with AUVA, Donaueschingenstrasse 13, A-1200 Vienna, Austria
6 Austrian Cluster for Tissue Regeneration, Donaueschingenstrasse 13, A-1200 Vienna, Austria
7 Faculty of Medicine, University of Ljubljana, Vrazov trg 2, 1000 Ljubljana, Slovenia
8 Faculty of Health Sciences, University of Primorska, Polje 42, 6310 Izola, Slovenia
9 University Hospital Sveti Duh, Department of Orthopaedic Surgery, Sveti Duh 64, 10000 Zagreb, Croatia
10 University of Applied Health Sciences, Mlinarska cesta 38, 10000 Zagreb, Croatia
Abstract
Muscle tissues attached to the proximal ends of hamstring tendon grafts are routinely discarded during anterior cruciate ligament (ACL) reconstruction. Preserving the muscle on the ACL graft was shown to improve the surgery outcomes, possibly due to the osteogenic differentiation of muscle satellite cells, accelerating graft integration into the underlying bone. The enhancement of muscle cell osteogenic differentiation was previously demonstrated via adenoviral transfer of bone morphogenetic protein-2 (BMP-2). We evaluated gene electrotransfer as a fast, non-viral and clinically relevant alternative for the delivery of plasmid DNA to muscle-tendon ACL grafts. Human muscle-tendon tissues remaining were collected from 13 patients undergoing ACL reconstruction procedures, and standardized tissue samples were injected twice with 20 µg plasmid DNA or not treated. A combination of high voltage (600 V, 100 µs) and low voltage (80 V, 100 ms) electric pulses or medium voltage (MV; 200 V, 20 ms) pulses were first tested using plasmid DNA encoding the green fluorescent protein. The selection of MV protocol was confirmed with a luciferase plasmid and subsequently used to test a therapeutic BMP-2 plasmid. Upon detailed evaluation of individual tissue sample properties (i.e., donors, thickness and volume) and their BMP-2 release, further optimization of tissue selection and preparation for gene electrotransfer was defined. This study indicates the feasibility of gene electrotransfer as a method to deliver plasmid DNA easily and rapidly to muscle tissue preserved on ACL grafts.
Graphical Abstract

Keywords
- Gene therapy
- plasmid DNA
- gene electrotransfer
- anterior cruciate ligament
