This invention features a method for eliciting an antioxidative effect. The method includes administering to a subject (e.g., an animal or human) in need thereof an effective amount of a tetrapyrrole compound of formula (I): Each of R, R, R<c>, R<d>, R<e>, R<f>, R<g>, and R<h>, independently, is H or alkyl; R1 is alkyl or CHO; R2 is alkyl; R3 and R4 taken together are part of a cyclyl or heterocyclyl ring, and R5 is (CH2)mCOOR, in which R is H, and m is 1, 2, or 3; or R3 is (CH2), COOR', C(O)(CH2)nCOOR', CH(OH)(CH2)nCOOR', and R4 and R5 taken together are part of a cyclyl or heterocyclyl ring, in which R' is H or alkyl, and n is 0, 1, 2, or 3; and R6 is alkenyl or CHO; the tetrapyrrole compound optionally being chelated with Mg<2+>, Mn<2+>, Cu<2+>, Fe<2+>, Co<2+>, Ni<2+>, or Zn<2+> through the nitrogen atoms on the four pyrrole rings.