Oxygen tension alters cartilage redox balance in response to traumatic impact

Redox balance plays a key role in cellular homeostasis. Disruption of redox balance contributes to initiation and progression of multiple diseases including osteoarthritis, a common joint disease that is characterized by progressive cartilage damage. Therefore, monitoring cartilage redox balance can be used to evaluate cartilage health and disease status. Previous studies have investigated the effect of oxygen tension and traumatic impact on cartilage redox balance separately, but their interplay is not well known. The aim of this study is to quantify time- and position-dependent peracute responses of cartilage redox balance to impact injury at controlled oxygen tension.

Optical redox imaging (ORI) was used to evaluate redox balance in porcine cartilage explants. ORI measures the autofluorescence from cofactors in cellular redox reactions to provide a real-time evaluation of redox balance. Porcine cartilage explants underwent traumatic impact at normal (room) or low oxygen tension, with imaging before and after loading. Samples were snap frozen shortly after imaging for gene expression analysis. Achieved loading parameters were calculated based on high-speed camera images.

At normal oxygen tension, fluorescent intensity increased after impact loading in both channel 1 (corresponding to reduced nicotinamide adenine dinucleotide (NADH) and its phosphate (NADPH)) and channel 2 (corresponding to flavin adenine dinucleotide (FAD)), but this effect was not observed at low oxygen tension. In addition, a significant temporal effect was only observed for optical redox ratio (reflecting the relative accumulation of the cofactors), which was elevated after 28 minutes post-impact. Despite the measured changes in redox, gene expression did not change significantly.

Low oxygen tension was protective against impact injury-induced autofluorescence changes. In addition, the response of cartilage redox balance to impact was progressive.