Effects of photodegradation of nifedipine on dog erythrocyte membranes

: We studied the effects of nifedipine (NF) on UV-induced photohemolysis of erythrocytes in vitro. A suspension in physiologic saline of crythrocytes separated from the venous blood sample freshly obtained from a dog was prepared and used. NF is a photolabile agent, and this drug was extremely sensitive to the long wavelength (365 nm) of UV light. The most abundant photodegradation product was a nitroso-derivative which changed into a lactam-derivative in the dog erythrocyte suspension with or without irradiation. NF itself showed protective effects against photohemolysis of erythrocytes caused by 365 nm of UV light as well as hypotonic hemolysis. But NF enhanced the degree of photohemolysis under oxygen condition. The photohemolysis enhanced by NF was reduced by thiobarbituric acid, indicating an oxidative stress by a radical intermediate of NF to photohemolysis. On the other hand, the nitroso-derivative reacted with erythrocyte hemoglobin spectroscopically to change into the lactam-derivative. It is considered that NF is a phototoxic agent to cause photohemolysis by producing a radical intermediate with oxygen and unknown species of hemoglobin degraded with the nitroso-derivative of nifedipine photoproduct.