Abstract
Mature articular cartilage is an avascular tissue characterized by a low oxygen environment. In joint disease, acidosis and further reductions in oxygen levels occur, compromising cartilage integrity.This study investigated how acidosis and very low oxygen levels affect components of the cellular redox system in equine articular chondrocytesand whether the antioxidants resveratrol and N-acetylcysteine could modulate this system. We used articular chondrocytes isolated from nondiseased equine joints and cultured them in a 3-D alginate bead system for 48h in <1, 2, 5, and 21% O2 at pH 7.2 or 6.2 in the absence or presence of the proinflammatory cytokine, interleukin-1β (10ng/ml).In addition, chondrocytes were cultured with resveratrol (10µM) or N-acetylcysteine (NAC) (2mM).Cell viability, glycosaminoglycan (GAG) release, mitochondrial membrane potential (ΔΨm), reactive oxygen species (ROS), GSH:GSSG ratio, and SOD1 and SOD2 protein expression were measured. Very low levels of oxygen (<1%), acidosis (pH 6.2), and exposure to IL-1β led to reductions in cell viability, increased GAG release, alterations in ΔΨm and ROS levels, and reduced GSH:GSSG ratio. In addition, SOD1 and SOD2 protein expressions were reduced. Both resveratrol and NAC partially restored ΔΨm and ROS levels and prevented GAG release and cell loss and normalized SOD1 and SOD2 protein expression. In particular NAC was highly effective at restoring the GSH:GSSG ratio.These results show that the antioxidants resveratrol and N-acetylcysteine can counteract the redox imbalance in articular chondrocytes induced by low oxygen and acidic conditions.