An embodiment of the invention provides a use of an effective amount of a transition metal complex of a corrole, an optically active isomer thereof, or a pharmaceutically acceptable salt thereof for treating a disease of the eye and/or the kidney in a subject suffering from diabetes. An embodiment of the invention further provides a use of a transition metal complex of a corrole, an optically active isomer thereof, or a pharmaceutically acceptable salt thereof for lowering serum glucose and serum triglyceride levels in a subject suffering from diabetes.