Discussions with Leaders: A Conversation Between Richard Wahl and Johannes Czernin

3 Objectives: As a common reactive oxygen species (ROS)-related renal disease, acute kidney injury (AKI) causes numerous deaths annually, and only supportive treatment is currently available in the clinics. The detrimental reactive oxygen species (ROS) that trigger oxidative stress and inflammation are believed to induce the AKI. Recent progress in nanomedicine has enabled the dramatic treatment of ROS-related diseases using the nano-antioxidants, which, however, are subject to uptake by the kidney due to the renal glomerular filtration barrier. Our goal is to exploit the nano-antioxidants with high renal accumulation and presenting therapeutic effect for AKI. Methods: The blue Mo-based polyoxometalate (POM) nanoclusters were found to exhibit broad antioxidative activities against multiple toxic ROS including H2O2, O2•−, and •OH, where the readily variable valence of Mo5+ and Mo6+ in POM plays an important role in scavenging ROS. The murine model of AKI was built through intramuscular injection of 50% glycerol into dehydrated normal mice. Two hours after induction of AKI,POM radiolabeled with 89Zr was intravenously injected into AKI mice. Longitudinal PET imaging was then performed at various time points to monitor the renal accumulation in vivo. The therapeutic efficacy against AKI in living animals was evaluated by a dynamic PET with 68Ga-EDTA, blood urea nitrogen and creatinine measurements, H&E staining of kidney tissues, and biomarkers detection (e.g., kidney injury molecule-1, heme oxygenase-1, level of superoxide dismutase, DNA damage, etc.) in the kidneys. Results: These ultra-small POM nanoclusters containing elements of Mo, O, and P were uniform with an average diameter of ca. 1 nm. The hydrated size of POM is below 10 nm, which meets the threshold for kidney filtration and thus are able to pass through. They exhibited high ROS (i.e., H2O2, O2•- and •OH) scavenging activity, which were confirmed both in solutions and on cells. PET imaging of AKI mice showed that these nanoclusters presented high and gradual accumulation in the injured kidneys at all examined time points after injection, and the renal uptake of 89Zr-POM at 24 h post-injection (p.i.) was 17.7 ± 3.1 %ID/g. Furthermore, the dynamic PET with 68Ga-EDTA, blood urea nitrogen and creatinine measurements, and H&E staining of kidney tissues revealed that these ultra-small nanoclusters could recover renal function in the AKI mice. The detection of ROS-related biomarkers in renal tissues revealed the anti-oxidative roles of POM nanoclusters in AKI mice, which were reduced to the levels observed in healthy mice. CONCLUSION: In summary, a novel multi-antioxidant in the form of POM nanoclusters for antioxidative therapy of AKI in living animals was presented. Our findings revealed that POM nanoclusters exhibited broad antioxidative activities against multiple toxic ROS including H2O2, O2•−, and •OH.With high renal uptake, these ultra-small nanoclusters displayed excellent therapeutic efficacy of AKI induced by ROS, which has been demonstrated by dynamic PET imaging with 68Ga-EDTA, blood urea nitrogen and creatinine measurements, H&E staining, and biomarkers detection of kidney tissues. The protective effect of POM nanoclusters against AKI in living animals suggests exploring their use for the treatment of AKI patients, as well as patients with other ROS-related diseases.