Abstract 10893: Dietary Nitrate Supplementation With Beetroot Juice Enhances Cardiac Autophagy Markers AMBRA-1 (Activating Molecule in Beclin-1-regulated Autophagy) and ATG-5 (Autophagy-related Gene 5): Protective Role Against Doxorubicin Cardiotoxicity

Background: Beetroot juice (BRJ) is a dietary supplement containing high levels of nitrate and other nutrients. We previously reported that oral intake of BRJ protects against cardiotoxicity of doxorubicin (DOX) - a widely used anticancer drug. BRJ diminished cell injury (indicated by significantly lower serum levels of cardiac troponin I) and ventricular dysfunction caused by DOX. However, it remains unknown if BRJ modulates cardiac autophagy - a critical endogenous cellular quality control and damaged organelles removal mechanism, particularly under DOX-induced cardiototoxic stress. Therefore, the current study is designed to determine if cardioprotective dose of BRJ affects cardiac autophagy. Methods: Adult male CF-1 mice were divided into 4 groups (n=3-4/group) to receive: 1) Saline (0.2 ml, IP); 2) DOX (15 mg/kg, IP); 3) BRJ (10 g BRJ extract per liter of drinking water provided for 13 days); and 4) BRJ+DOX (BRJ for 7 days before DOX injection on Day 8 and throughout the 5-day post-DOX period. On Day 13, heart tissue samples were collected for determining the key autophagy markers with real-time PCR or Western blots. Results: Cardiac protein expression of AMBRA-1 (Fig. A) and ATG-5 (Fig. C) was significantly enhanced by BRJ with or without DOX co-treatment (P<0.05). Interestingly, BRJ intake also significantly augmented mRNA levels of AMBRA-1 (Fig. B) and ATG-5 (Fig. D) in BRJ+DOX group. Furthermore, the ratio of LC3B-II/LC3B-I, another hallmark for autophagy was decreased in DOX group, but restored in BRJ+DOX group to the level of Saline control group. Conclusions: BRJ intake significantly upregulates several key molecular markers of cardiac autophagy such as AMBRA-1 and ATG-5, which may contribute to BRJ-induced protection against DOX cardiotoxicity. The autophagy-related novel molecular mechanisms revealed in this study may provide a new rationale for potential use of BRJ as a safe nutraceutical therapy in reducing cardiotoxicity caused by DOX chemotherapy.