Dual action molecules: Bioassays of combined novel antioxidants and angiotensin II receptor antagonists

In this study we have investigated the in vitro angiotensin II receptor antagonist and antioxidant activity of a series of compounds in which the antioxidant pharmacophores (selenium, phenol, benzothiophene, ebselen or nitroxide) have been incorporated into the AT1 receptor antagonist (sartan) milfasartan. Activity of these compounds was assessed in tissue-based assays. The novel molecules (30 nM), nitrasartan or phenol-milfasartan, retained AT1 receptor antagonist potency in rat isolated right atria. Antioxidant capacity of the substituted sartans was examined in an AAPH (2,2′-azobis (2-amidinopropane) hydrochloride)-induced haemolysis assay (mouse C57/BL6 isolated erythrocytes). Each of the antioxidant pharmacophores (10 μM), except benzothiophene, protected against radical-mediated lysis. Of the novel sartans, only analogues incorporating selenium, phenol or nitroxide (nitrasartan) protected against radical-induced haemolysis. In the tissue-based assay using mouse isolated paced left atria, the free radical generator doxorubicin (30 μM) resulted in a decrease in left atrial force over 90 min. In this assay the phenol, nitroxide or ebselen antioxidant pharmacophores protected against doxorubicin-induced negative inotropy but selenocystine and benzothiophene did not. Nitrasartan (10 μM) was the only novel analogue to protect against radical-induced negative inotropy. Nitrasartan also antagonised angiotensin II responses and decreased superoxide production in a concentration-dependent manner in rat isolated carotid arteries and aortae, respectively. In conclusion, nitrasartan is a dual action molecule demonstrating both AT1 receptor antagonist potency and antioxidant properties in vitro.