gms | German Medical Science

Objectives: Gene therapy is an attractive strategy for the durable treatment of human osteoarthritis (OA), a gradual, irreversible joint disease. Gene carriers based on the small human adeno-associated virus (AAV) exhibit major efficacy in modifying damaged human articular cartilage in situ over extended periods of time. Still, the use of such vectors in vivo is impaired by the presence of neutralizing antibodies against viral capsid elements in a majority of patients. Controlled delivery of rAAV via smart nanomaterials is a potent approach to overcome such limitations. Carbon dots (CDs) are a relatively new class of nanocarriers capable of efficiently delivering plasmid DNA in several cell lines. Here, for the first time we report the feasibility of transferring rAAV vectors via carbon dots to human articular chondrocytes.

Methods: rAAV-lacZ vectors carrying the E. coli β -galactosidase gene (lacZ) controlled by the CMV-IE promoter/enhancer. Human OA articular chondrocytes (hOACs) were isolated from human OA cartilage tissue explants obtained from the joint of patients undergoing total knee arthroplasty. For the experiments, four CDs (MC136, MC148, MC316, and MM276A) were generated through pyrolysis of citric acid. CDs were mixed with rAAV-lacZ vectors in equal parts and incubated for 30 min prior to application to monolayer cultures of hOACs (3,000 cells/well). Control conditions included untreated cells (negative control), cells treated with CDs lacking rAAV (CD controls), and rAAV in free form (positive control). Transgene expression was monitored by X-Gal staining and using the Beta-Glo® Assay System (Promega). Cell viability during the culture period was quantified by using the Cell Proliferation reagent WST-1 (Roche Applied Science). Each condition was performed in duplicate in two independent experiments. The t-test was employed with P ≤ 0.05 considered statistically significant.

Results and conclusion: Delivery of rAAV (lacZ) using the various CDs resulted in an increased modification of hOACs relative free vector treatment (up to 2.6-fold difference, P ≤ 0.030). Interestingly, while MC316 was the most effective compound to increase rAAV-mediated gene transfer efficiencies early on (day 1: 2.1-fold difference versus free vector treatment, P ≤ 0.044), MM276A led to a more sustained gene transfer overtime (day 10: 2.6-fold difference versus free vector treatment, P ≤ 0.030). An evaluation of the levels of cell survival overtime revealed values of viability of 100% upon administration of rAAV in its free form or delivered via MC136 and MC148 CDs. In contrast, administration of rAAV-lacZ via MC316 or MM276 resulted in marked decreases in cell viability to values close to 25% (P ≤ 0.05). The same tendency was observed upon treatment of the cells with the different CDs lacking rAAV (not shown). Delivery of rAAV-lacZ via CDs (MC136, MC148) to hOACs resulted in increased and prolonged levels of transgene expression, without detrimental effects on cell viability.