Oxidative stress (OS) is defined as reactive oxygen species (ROS; e.g., free radicals) in excess of antioxidant defense mechanisms. Antioxidants are substances that can delay or prevent oxidation of a target molecule. OS can occur due to an excess ofROS, a reduction in antioxidants, or both. Damage due to OS has been associated with all major age-related diseases in people. OS has also been documented in several conditions in dogs and cats. OS may also play a role in joint disease. Matrix metalloproteinases, which are involved in degradation of the extracellular matrix in joint cartilage, can be activated by ROS. A deficiency in extracellular superoxide dismutase (SOD), which binds to the negatively charged glycoproteins and collagen of the extracellular matrix of tissues and may be the major antioxidant in cartilage, contributes to the clinical signs associated with osteoarthritis.
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