Aims: Oxidative stress and mitochondrial dysfunction participate together in the development of heart failure (HF). mRNA levels of monoamine oxidase-A (MAO-A), a mitochondrial enzyme that produces hydrogen peroxide (H 2 O 2 ), increase in several models of cardiomyopathies. Therefore, we hypothesized that an increase in cardiac MAO-A could cause oxidative stress and mitochondrial damage, leading to cardiac dysfunction. In the present study, we evaluated the consequences of cardiac MAO-A augmentation on chronic oxidative damage, cardiomyocyte survival, and heart function, and identified the intracellular pathways involved. Results: We generated transgenic (Tg) mice with cardiac-specific MAO-A overexpression. Tg mice displayed cardiac MAO-A activity levels similar to those found in HF and aging. As expected, Tg mice showed a significant decrease in the cardiac amounts of the MAO-A substrates serotonin and norepinephrine. This was associated with enhanced H 2 O 2 generation in situ and mitochondrial DNA oxidation. As a consequence, MAO-A Tg mice demonstrated progressive loss of cardiomyocytes by necrosis and ventricular failure, which were prevented by chronic treatment with the MAO-A inhibitor clorgyline and the antioxidant N-acetyl-cystein. Interestingly, Tg hearts exhibited p53 accumulation and downregulation of peroxisome proliferator-activated receptor-c coactivator-1a (PGC-1a), a master regulator of mitochondrial function. This was concomitant with cardiac mitochondrial ultrastructural defects and ATP depletion. In vitro, MAO-A adenovirus transduction of neonatal cardiomyocytes mimicked the results in MAO-A Tg mice, triggering oxidative stress-dependent p53 activation, leading to PGC-1a downregulation, mitochondrial impairment, and cardiomyocyte necrosis. Innovation and Conclusion: We provide the first evidence that MAO-A upregulation in the heart causes oxidative mitochondrial damage, p53-dependent repression of PGC-1a, cardiomyocyte necrosis, and chronic ventricular dysfunction. Antioxid. Redox Signal. 18, 5-18.

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Inhibition of the mitochondrial permeability transition pore (PTP) has proved to be an effective strategy for preventing oxidative stress-induced cell death, and the pore represents a viable cellular target for drugs. Here, we report that inhibition of complex I by rotenone is more effective at PTP inhibition than cyclosporin A in tissues that express low levels of the cyclosporin A mitochondrial target, cyclophilin D; and, conversely, that tissues in which rotenone does not affect the PTP are characterized by high levels of expression of cyclophilin D and sensitivity to cyclosporin A. Consistent with a regulatory role of complex I in the PTP-inhibiting effects of rotenone, the concentrations of the latter required for PTP inhibition precisely match those required to inhibit respiration; and a similar effect is seen with the antidiabetic drug metformin, which partially inhibits complex I. Remarkably (i) genetic ablation of cyclophilin D or its displacement with cyclosporin A restored PTP inhibition by rotenone in tissues that are otherwise resistant to its effects; and (ii) rotenone did not inhibit the PTP unless phosphate was present, in striking analogy with the phosphate requirement for the inhibitory effects of cyclosporin A [Basso et al. (2008) J. Biol. Chem. 283, 26307-26311]. These results indicate that inhibition of complex I by rotenone or metformin and displacement of cyclophilin D by cyclosporin A affect the PTP through a common mechanism; and that cells can modulate their PTP response to complex I inhibition by modifying the expression of cyclophilin D, a finding that has major implications for pore modulation in vivo.

N eonatal hypoxia-ischemia is a common cause of neonatal brain injury and results in cerebral palsy, learning disabilities, and epilepsy.1 In addition to global cerebral ischemia arising from systemic asphyxia, recent data suggest a higher incidence of focal ischemia-reperfusion leading to stroke in near-term neonates.2 Tissue-type plasminogen activator is the only approved agent capable of improving reperfusion after ischemia in the adult brain. 3 However, no safe neuroprotective molecule is currently available to protect the immature brain.Among vasoactive molecules, nitric oxide (NO) is a small, highly diffusible and reactive molecule produced by the NO synthases and released from endothelial cells 4 and perivascular nitrergic neurons. 5,6 Endogenous NO is widely recognized as an important messenger and effector molecule for vascular tone and tolerance to damage as well as a mediator in a variety of acute and chronic inflammatory systems. 7 NO is also involved in several critical processes in the developing brain; indeed, exposure to inhaled NO (iNO) during the first week of postnatal life has recently been shown to play a key role in myelination in the developing brain 8 and to significantly reduce the size of excitotoxic lesions in neonatal rat pups. 9 We recently demonstrated, by using 2-dimensional color-coded pulsed ultrasound imaging, that collateral recruitment or failure during ischemia, as revealed by changes in blood flow velocities in the basilar trunk (BT), determined the extent of the ischemic lesion in P7 rats 10 and wasBackground and Purpose-We recently demonstrated that endogenous nitric oxide (NO) modulates collateral blood flow in a neonatal stroke model in rats. The inhalation of NO (iNO) has been found to be neuroprotective after ischemic brain damage in adults. Our objective was to examine whether iNO could modify cerebral blood flow during ischemiareperfusion and reduce lesions in the developing brain. Methods-In vivo variations in cortical NO concentrations occurring after 20-ppm iNO exposure were analyzed using the voltammetric method in P7 rat pups. Inhaled NO-mediated blood flow velocities were measured by ultrasound imaging with sequential Doppler recordings in both internal carotid arteries and the basilar trunk under basal conditions and in a neonatal model of ischemia-reperfusion. The hemodynamic effects of iNO (5 to 80 ppm) were correlated with brain injury 48 hours after reperfusion. Results-Inhaled NO (20 ppm) significantly increased NO concentrations in the P7 rat cortex and compensated for the blockade of endogenous NO synthesis under normal conditions. Inhaled NO (20 ppm) during ischemia increased blood flow velocities and significantly reduced lesion volumes by 43% and cellular damage. In contrast, both 80 ppm iNO given during ischemia and 5 or 20 ppm iNO given 30 minutes after reperfusion were detrimental. Blood flow increases in the BT mirror the efficiency of collateral support through the circle of Willis and the opening of cortical arterial anastomoses among anter...

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Biochemical approaches were used in freely moving rats to determine, under steady-state conditions, the brain/arterial plasma partition coefficients of L-tryptophan and ␣-[ 3 H]methyl-L-tryptophan, from which the lumped constant for the ␣-methyl-L-tryptophan method of estimating the rate of brain serotonin synthesis is calculated. The lumped constants were significantly different in the various structures examined: 0.149 Ϯ 0.003 in the raphe dorsalis, 0.103 Ϯ 0.002 in the raphe centralis, 0.087 Ϯ 0.003 in the reticular formation, and 0.62 Ϯ 0.08 in the pineal gland. From these data we proposed a two-compartment model to calculate the rate of serotonin synthesis by quantitative autoradiography using a three-time point experiment. Rates of synthesis for the raphe dorsalis and the reticular formation (620 Ϯ 57 and 80 Ϯ 35 pmol/g of tissue/min, respectively) were similar to those measured simultaneously by biochemical means, but rates were 50% higher for the raphe centralis (568 Ϯ 90 vs. 381 Ϯ 31 pmol/g of tissue/min). The lack of dynamic equilibrium of the tracer between plasma and tissue pools may explain the discrepancy between the two methods. Our findings did not confirm previous data, indicating that the application of the autoradiographic method to measure the rate of brain serotonin synthesis using ␣-methyl-L-tryptophan as tracer has limitations. Key Words: Serotonin synthesis-Lumped constant-␣-Methyl-L-tryptophan-Brain-Rat.

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Cyclosporine A normalized ROS production, decreased inflammation, and restored mitochondrial coupling during aortic cross-clamping. Incomplete Vmax protection might be due to low cyclophilin D expression in gastrocnemius, preventing CsA from blocking mPTP opening.