In vitro antioxidant capacity and antigenotoxic properties of protoporphyrin and structurally related tetrapyrroles

The antioxidant properties of protoporphyrin IX and related tetrapyrroles are poorly characterized. Therefore, eight tetrapyrroles, five of which are produced in vivo, were tested to assess their antioxidant capacities in the Salmonella reverse mutation, TEAC, FRAP and ORAC assays. Tertiary-butyl hydroperoxide (tert-BOOH) in the presence or absence of metabolic activation (±S9) was added to Salmonella strain TA102 together with the test compounds. In the absence of metabolic activation, the order of effectiveness was protoporphyrin > biliverdin > bilirubin ditaurate > bilirubin > biliverdin dimethyl ester > stercobilin > bilirubin dimethyl ester > urobilin. In the presence of S9, the effectiveness was reversed, with urobilin > biliverdin dimethyl ester > bilirubin dimethyl ester > stercobilin > biliverdin > bilirubin > bilirubin ditaurate > protoporphyrin. In the antioxidant capacity assays FRAP, TEAC and ORAC, mainly bilirubin, bilirubin ditaurate, biliverdin and protoporphyrin showed antioxidant activity. This study reports that previously untested tetrapyrroles of related structure prevent oxidatively induced genotoxicity, and for some, novel underlying mechanisms of antioxidant action were revealed. These results support the physiological importance and biological relevance of tetrapyrroles including protoporphyrin that might act as antioxidants, protecting from oxidatively induced DNA damage, particularly in the tissues/organs where they accumulate.