Interaction between sodium tanshinone IIA sulfonate and the adriamycin semiquinone free radical: A possible mechanism for antagonizing adriamycin-induced cardiotoxity

Adriamycin (ADR) is a powerful and widely used antitumor drug, but its dose dependent cardiotoxicity limits its application. This side effect is believed to be caused by the adriamycin semiquinone free radical (ASFR). The primary focus of this work is to test effects of sodium tanshinone IIA sulfonate (STS) on ASFR and adriamycin–induced lipid peroxidation. It was found that ADR, whether in the system of heart homogenate, heart mitochondria or heart submitochondria, with NADH as the substrate or in xanthine/xanthine oxidase under anaerobic conditions, all produced ASFR rapidly. STS was shown to effectively scavenge ASFR in all these systems and postpone the appearance of ASFR. The delayed time was proportional to the amount of STS. Under aerobic conditions, ASFR could be oxidized to generate oxygen free radicals. STS could not scavenge these oxygen free radicals, but it could effectively scavenge lipid free radicals generated from membrane lipid peroxidation of heart mitochondria. STS could significantly reduce mitochondrial swelling and lipid peroxidation induced by ADR. Animal experiments show that treatment of STS could inhibit endogenous lipid peroxidation caused by ADR. Here, a protective mechanism of STS is suggested that STS can rapidly and univalently oxidize ASFR, causing the cycle of adriamycin between its quinone form and semiquinone form and inhibiting the accumulation of ASFR. Under aerobic condition, STS can protect heart mitochondria by scavenging lipid free radicals generated from adriamycin-induced mitochondrial lipid peroxidation. This investigation shows that STS may be a physiological drug to antagonize the cardiotoxicity of ADR.