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Background and Purpose Spermidine, a natural polyamine, is abundant in mammalian cells and is involved in cell growth, proliferation, and regeneration. Recently, oral spermidine supplements were cardioprotective in age‐related cardiac dysfunction, through enhancing autophagic flux. However, the effect of spermidine on myocardial injury and cardiac dysfunction following myocardial infarction (MI) remains unknown. Experimental Approach We determined the effects of spermidine in a model of MI, Sprague–Dawley rats with permanent ligation of the left anterior descending artery, and in cultured neonatal rat cardiomyocytes (NRCs) exposed to angiotensin II (Ang II). Cardiac function in vivo was assessed with echocardiography. In vivo and in vitro studies used histological and immunohistochemical techniques, along with western blots. Key Results Spermidine improved cardiomyocyte viability and decreased cell necrosis in NRCs treated with angiotensin II. In rats post‐MI, spermidine reduced infarct size, improved cardiac function, and attenuated myocardial hypertrophy. Spermidine also suppressed the oxidative damage and inflammatory cytokines induced by MI. Moreover, spermidine enhanced autophagic flux and decreased apoptosis both in vitro and in vivo. The protective effects of spermidine on cardiomyocyte apoptosis and cardiac dysfunction were abolished by the autophagy inhibitor chloroquine, indicating that spermidine exerted cardioprotective effects at least partly through promoting autophagic flux, by activating the AMPK/mTOR signalling pathway. Conclusions and Implications Our findings suggest that spermidine improved MI‐induced cardiac dysfunction by promoting AMPK/mTOR‐mediated autophagic flux.

Watershed urbanization leads to dramatic changes in draining streams, with urban streams receiving a high frequency of scouring flows, together with the nutrient, contaminant, and thermal pollution associated with urbanization. These changes are known to cause significant losses of sensitive insect and fish species from urban streams, yet little is known about how these changes affect the composition and function of stream microbial communities. Over the course of two years, we repeatedly sampled sediments from eight central North Carolina streams affected to varying degrees by watershed urbanization. For each stream and sampling date, we characterized both overall and denitrifying bacterial communities and measured denitrification potentials. Denitrification is an ecologically important process, mediated by denitrifying bacteria that use nitrate and organic carbon as substrates. Differences in overall and denitrifying bacterial community composition were strongly associated with the gradient in urbanization. Denitrification potentials, which varied widely, were not significantly associated with substrate supply. By incorporating information on the community composition of denitrifying bacteria together with substrate supply in a linear mixed-effects model, we explained 45% of the variation in denitrification potential (p-value<0.001). Our results suggest that (1) the composition of stream bacterial communities change in response to watershed urbanization and (2) such changes may have important consequences for critical ecosystem functions such as denitrification.

Given the demonstrated antimicrobial properties of silver nanoparticles (AgNPs), and the key role that microorganisms play in performing critical ecosystem functions such as decomposition and nutrient cycling, there is growing concern that AgNP pollution may negatively impact ecosystems. We examined the response of streamwater and sediment microorganisms to commercially available 21 ± 17 nm AgNPs, and compared AgNP impacts to those of dissolved-Ag added as AgNO(3). We show that in streamwater, AgNPs and AgNO(3) decreased respiration in proportion to dissolved-Ag concentrations at the end of the incubation (r(2) = 0.78), while in sediment the only measurable effect of AgNPs was a 14 % decrease in sulfate concentration. This contrasts with the stronger effects of dissolved-Ag additions in both streamwater and sediment. In streamwater, addition of dissolved-Ag at a level equivalent to the lowest AgNP dose led to respiration below detection, a 55 % drop in phosphatase enzyme activity, and a 10-fold increase in phosphate concentration. In sediment, AgNO(3) addition at a level equivalent to the highest AgNP addition led to a 34 % decrease in respiration, a 55 % increase in microbial biomass, and a shift in bacterial community composition. The results of this study suggest that, in similar freshwater environments, the short-term biological impacts of AgNPs on microbes are attenuated by the physical and chemical properties of streamwater and sediment.