Tolerance to NADH/NAD+ imbalance anticipates aging and anti-aging interventions

SummaryRedox couples coordinate cellular function, but the consequences of their imbalances are unclear. This is somewhat associated with the limitations of their experimental quantification. Here we circumvent these difficulties by presenting a new approach that characterizes fitness-based tolerance profiles to redox couple imbalances using an in silico representation of metabolism. Focusing on the NADH/NAD+ redox couple in yeast, we demonstrate that reductive disequilibria generate metabolic syndromes comparable to those observed in cancer cells. The tolerance of yeast mutants to redox disequilibrium can also explain 30% of the variability in their experimentally measured chronological lifespan. Moreover, by predicting the significance of some metabolites to help stand imbalances, we correctly identify nutrients underlying mechanisms of pathology, lifespan-protecting molecules or caloric restriction mimetics. Tolerance to redox imbalances becomes thus a valid framework to recognize fundamental properties of the aging phenotype while providing a firm biological rationale to assess anti-aging interventions.

Benthic perspective on Earth’s oldest evidence for oxygenic photosynthesis

The Great Oxidation Event (GOE) is currently viewed as a protracted process during which atmospheric oxygen increased above ∼10−5 times the present atmospheric level (PAL). This threshold represents an estimated upper limit for sulfur isotope mass-independent fractionation (S-MIF), an Archean signature of atmospheric anoxia that begins to disappear from the rock record at 2.45 Ga. However, an increasing number of papers have suggested that the timing for oxidative continental weathering, and by conventional thinking the onset of atmospheric oxygenation, was hundreds of million years earlier than previously thought despite the presence of S-MIF. We suggest that this apparent discrepancy can be resolved by the earliest oxidative-weathering reactions occurring in benthic and soil environments at profound redox disequilibrium with the atmosphere, such as biological soil crusts and freshwater microbial mats covering riverbed, lacustrine, and estuarine sediments. We calculate that oxygenic photosynthesis in these millimeter-thick ecosystems provides sufficient oxidizing equivalents to mobilize sulfate and redox-sensitive trace metals from land to the oceans while the atmosphere itself remained anoxic with its attendant S-MIF signature. As continental freeboard increased significantly between 3.0 and 2.5 Ga, the chemical and isotopic signatures of benthic oxidative weathering would have become more globally significant from a mass-balance perspective. These observations help reconcile evidence for pre-GOE oxidative weathering with the history of atmospheric chemistry, and support the plausible antiquity of a terrestrial biosphere populated by cyanobacteria well before the GOE.

Abstract 39: Organic Nitrates Improve Calcium Handling and Myofilament Sensitivity Impaired by Nitroso-Redox Disequilibrium

Oxidative stress is a key factor in the dysfunctional calcium (Ca 2+ ) handling and contractile performance in heart disease. Organic nitrates are used for the treatment of cardiovascular afflictions, however endogenous nitric oxide (NO) has a broad spectrum of actions and the mechanisms by which it regulates Ca 2+ cycling and contractility is poorly understood. Neuronal NO synthase (nNOS) deficiency induces a nitroso-redox disequilibrium characterized by oxidative stress and altered contractility and calcium handling. We hypothesize that treatment of nNOS −/− mice with organic nitrates such as nitroglycerin (TNG) or isosorbide dinitrate (ISDN) reduces cytosolic calcium levels and restores myofilament responsiveness to calcium with no changes in contractility. Cardiomyocytes (CMs) were isolated from nNOS −/− (N=7) and wild type (WT) mice (N=3). Cells were loaded with fura-2 and then electrically evoked intracellular Ca 2+ and sarcomere length were simultaneously measured in an IonOptix system. It has been shown that L-type Ca 2+ current is exacerbated in nNOS −/− cardiomyocytes. In consequence, at 1 Hz pacing rate, Ca 2+ peak and transient amplitude were increased in nNOS −/− (Peak Ca 2+ : 571 ± 38 nM) compared to WT (401 ± 32 nM; p = 0.012) cardiomyocytes, which was reduced toward normal by 10 nmol/L TNG (453 ± 55 nM; p = 0.11) as well as 10 nmol/L ISDN (394 ± 65; p = 0.035). Phospholamban phosphorylation has been shown to be reduced in nNOS −/− CMs, possibly due to the enhanced activity of protein phosphatases induced by oxidative stress. Thus, Ca 2+ decay and sarcomere relaxation were slower in nNOS −/− compared to WT CMs ( p < 0.0001). Treatment with TNG ( p < 0.0001 vs. NOS1 −/− ) or ISDN ( p < 0.0001 vs. NOS1 −/− ) accelerated Ca 2+ decay and relaxation. Ca 2+ sensitivity was impaired in nNOS −/− ( p < 0.021 vs. WT). Although organic nitrates either reduce or do not affect myofilament sensitivity in normal myocytes, TNG and ISDN increased their responsiveness to Ca 2+ in nNOS −/− . In conclusion, restoration of NO availability and subsequent attenuation of the nitroso-redox imbalance, improved excitation-contraction coupling in nNOS −/− CMs, decreased intracellular Ca 2+ which is counteracted by the improved myofilament sensitivity resulting in no net change in contractility.

Alteration of Repository Structural Materials Within the First Few Years

ABSTRACTA series of batch laboratory experiments were set up to study the gross effects of microbial activity on repository geochemistry, radionuclide sorption and integrity of repository and host rock materials. The experiments were fully monitored for 550 days and some were continued, under apparently aerobic conditions, for 1700 days. Geochemical modelling of the experiments reproduced many of their features, but showed that the contents were not in chemical equilibrium after 1700 days with redox disequilibrium a likely feature. The models could not predict localised reactions such as enhanced pitting of steel which appeared to be microbially mediated.