Antibodies with superoxide dismutase activity in health and diseases associated with oxidative stress

It is not widely appreciated that antibodies of the immune system have structural homology with the enzyme antioxidant copper-zinc superoxide dismutase (CuZnSOD). Whilst enhanced superoxide dismutase activity of antibodies (AbSOD activity) has been detected at acidic pH (6.45) in atherosclerotic lesions, AbSOD activity has not been investigated in other disease states associated with oxidative stress and immune dysfunction. This research aimed to determine the effect of pH changes on AbSOD activity, and antioxidant and oxidative stress markers in different disease states. Initial laboratory experiments investigated an antibody with reported AbSOD activity (HSA-9). Protein A agarose was used to purify the antibody, and electrophoresis and western blotting were performed. It was confirmed IgG-antibodies were the cause of superoxide dismutase activity (SOD activity) and CuZnSOD association was excluded. Additionally, a superoxide dismutase activity assay was optimised for the detection of AbSOD activity. In an investigation of the pH dependency of CuZnSOD, and human and mouse IgG antibodies it was observed that CuZnSOD activity was independent of pH (5.5 – 8.0). AbSOD activity of IgG was optimal at acidic pH (5.5 – 6.5). Pro-oxidant activity of antibodies (AbPro activity) was detected upon prolonged exposure to superoxide, which was optimal at pH 7.5. An exploratory observational study was performed on 59- patients compared to 19- ‘healthy’ controls. The pH dependency of AbSOD activity was investigated for antibodies isolated from the serum of patients with rheumatoid arthritis (RA), coeliac disease (CD), myocardial infarction (MI), breast cancer (BC), monoclonal gammopathy of unknown significance (MGUS) and myeloma (MM). Furthermore, patients’ serum catalase (ng/mL and U/mL), serum SOD (ng/mL and U/mL), and serum hydroperoxide (µmol H2O2 equivalents/L) were studied. Observed AbSOD activity was significantly increased in RA and MI at pH 5.5 and in myeloma between pH 6.0 – 7.4. Upon prolonged exposure to superoxide AbPro activity was decreased between pH 6.5 – 7.4 in myeloma. In conclusion, this is the first report that AbSOD activity is increased at pH 5.5 in rheumatoid arthritis and myocardial infarction and is increased in myeloma between pH 6.0 – 7.4, compared to ‘healthy’ controls. AbSOD activity may confer antioxidant protection at sites of oxidative stress and inflammation, however more research into the pH dependency of peroxidases, and the potential of antibody-generated hydrogen peroxide in immune signalling is required. This research provides novel evidence that AbSOD activity may have a role in monoclonal gammopathies, autoimmune diseases and cardiovascular diseases.