PubMed Health⌕ Search

Biomedical subjects

Alberto Boveris

Publications and source records attributed to Alberto Boveris.

At least 19 recordsLinked to original sources
PubMed2007

Oxygen delivery to the tissues and mitochondrial respiration.

In mammals, the O2 transport from the inspired air to the tissues is made by convective and diffusive mechanisms. The convective mechanisms are provided by the cardio-respiratory system and comprised by the basic variables of cardiac output and blood O2 content. Microcirculation in arterioles and capillaries is adjusted to match the O2 demand of local tissues. Endothelium-generated NO diffuses to the smooth muscle of microvessels and produces vasodilation that increases circulatory time in the capillaries and allows a more effective O2 extraction in the tissues. Once within the tissue, O2 diffuses to mitochondria where it is reduced in an exergonic process coupled to ATP synthesis. Both, O2 and ATP are the two most homeostatic intracellular species. In heart and muscle, both species show unchanged levels with 25-100 times increases in work load and ATP turnover rate. The linear rates of O2 uptake shown by tissue slices and perfused organs are interpreted as a fast switching of mitochondria between metabolic state 3 (with a fast rate of O2 uptake and ATP synthesis) and state 4 (with a slow rate of O2 uptake and no ADP phosphorylation). Endogenous mitochondrial NO, produced by mtNOS, sustains the concept of a physiological functional activity of this enzyme in regulating mitochondrial and cellular O2 uptake.

Animals↗
PubMed2007

Brain mitochondrial dysfunction in aging: conditions that improve survival, neurological performance and mitochondrial function.

Mice with (a) high spontaneous neurological activity, or subjected to (b) moderate exercise or (c) dietary supplemented with high doses of vitamin E from 28 weeks of age to senescence (76 wk of age), showed an increased survival and a retardation in the development of the neurological deficits associated to aging. During aging there was an increase in dysfunctional brain mitochondria, characterized by an increased content of oxidation products and by a diminished functional activity. The mitochondrial oxidative damage observed in adult (52 wk) and senescent mice (76 wk) was partially ameliorated in the groups of animals subject to the mentioned experimental conditions, and this decrease in mitochondrial oxidative damage was related to the improvement in neurological performance. In brain mitochondria, the activities of enzymes that are critical for mitochondrial function (mtNOS, NADH-dehydrogenase, and cytochrome oxidase) decreased progressively during aging and constituted aging markers. Usual clinical recommendations for aged humans, such as increased neurological activity, moderate exercise, and vitamin E supplementation, proved to be effective in increasing mice survival and neurological performances, along with a better mitochondrial function and a lower content of oxidation products.

Aging↗
PubMed2007

Mitochondrial nitric oxide synthase, a voltage-dependent enzyme, is responsible for nitric oxide diffusion to cytosol.

The mitochondrial metabolic state regulates the rate of mitochondrial NO production and release to the cytosol. Nitric oxide release of rat heart mitochondria decreased markedly from 2.2 to 1.2 nmol NO/min. mg protein in the state 4 to state 3 transition. The activity of mtNOS, responsible for NO release, is driven by the membrane potential and not by intramitochondrial pH changes. The release of NO by rat liver mitochondria showed an exponential dependence on membrane potential. A similar behavior was reported for heart mitochondrial H2O2 production. The fraction of heart cytosolic NO provided by diffusion from mitochondria is 90%. The intramitochondrial concentrations of L-arginine and NADPH are higher than their KM values, and the changes in their concentrations in the state 4-state 3 transition are not enough to explain the changes in NO release. These data indicate that the redox state of the respiratory chain components regulates H2O2 production and mitochondrial membrane potential modulates NO release, and support the speculation that NO and H2O2 are a biological signal that reports a high mitochondrial energy charge to the cytosol. The marked regulation of mtNOS activity, as a voltage-dependent enzyme and at the physiological range of membrane potentials, makes mtNOS a highly sensitive enzyme that in turn regulates mitochondrial O2 uptake and H2O2 production.

Animals↗
PubMed2007

Dietary thioproline decreases spontaneous food intake and increases survival and neurological function in mice.

Male mice on a diet supplemented with thioproline (l-thiazolidine-4-carboxylic acid), a physiological metabolite of 5-hydroxytryptamine, at 2.0 g/kg of food from 28 weeks of age and for their entire life, showed a 23-29% increased median and maximal life span. These survival increases were associated with improved neurological functions. Compared to control mice, thioproline-supplemented mice had a 20% lower integral spontaneous food intake, and 10% lower body weight at 100 weeks of age. Body weight showed a statistically significant inverse relationship with survival and neurological performances. Thioproline-supplemented mice exhibited a 58-70% decrease of the age-dependent oxidative damage in brain and liver mitochondria at 52 weeks (old mice) and 78 weeks (senescent mice) of age, respectively. The age-associated decrease of brain mitochondrial enzyme activities, NADH-dehydrogenase, cytochrome c oxidase, and mitochondrial nitric oxide synthase (mtNOS), in old and senescent mice were markedly prevented (51-74%) by thioproline. In vitro, thioproline neither exhibited direct antioxidant activity nor had any effect on the electron transfer or mtNOS functional activities of brain and liver mitochondria. It is surmised that thioproline induces an anorexic effect associated with improved survival and neurological function through a decreased oxidative damage and regulation that may involve hypothalamic appetite centers.

Age Factors↗
PubMed2006

The mitochondrial energy transduction system and the aging process.

Aged mammalian tissues show a decreased capacity to produce ATP by oxidative phosphorylation due to dysfunctional mitochondria. The mitochondrial content of rat brain and liver is not reduced in aging and the impairment of mitochondrial function is due to decreased rates of electron transfer by the selectively diminished activities of complexes I and IV. Inner membrane H(+) impermeability and F(1)-ATP synthase activity are only slightly affected by aging. Dysfunctional mitochondria in aged rodents are characterized, besides decreased electron transfer and O(2) uptake, by an increased content of oxidation products of phospholipids, proteins and DNA, a decreased membrane potential, and increased size and fragility. Free radical-mediated oxidations are determining factors of mitochondrial dysfunction and turnover, cell apoptosis, tissue function, and lifespan. Inner membrane enzyme activities, such as those of complexes I and IV and mitochondrial nitric oxide synthase, decrease upon aging and afford aging markers. The activities of these three enzymes in mice brain are linearly correlated with neurological performance, as determined by the tightrope and the T-maze tests. The same enzymatic activities correlated positively with mice survival and negatively with the mitochondrial content of lipid and protein oxidation products. Conditions that increase survival, as vitamin E dietary supplementation, caloric restriction, high spontaneous neurological activity, and moderate physical exercise, ameliorate mitochondrial dysfunction in aged brain and liver. The pleiotropic signaling of mitochondrial H(2)O(2) and nitric oxide diffusion to the cytosol seems modified in aged animals and to contribute to the decreased mitochondrial biogenesis in old animals.

Aging↗
PubMed2006

Autonomic regulation of pacemaker activity: role of heart nitric oxide synthases.

In autonomic-blocked rats treated with NG-nitro-L-arginine methyl ester (L-NAME, 7.5 mg/kg), heart rate increased 18% and mean arterial pressure increased 48%. Thyroidectomy, along with autonomic blockade, hampered the chronotropic response but did not modify the effect on blood pressure. After 150 min of autonomic blockade, the experimental end point, total nitric oxide (NO) production by heart NO synthases (NOS) decreased 61%: from 54 to 21 nmol NO.min-1.g heart-1. Mitochondrial NOS (mtNOS) and sarcoplasmic reticulum endothelial NOS activities decreased 74% and 52%, respectively. Mitochondria isolated from whole heart showed a well-coupled oxidative phosphorylation with high respiratory control and ADP-to-O ratios, decreased mtNOS activity (55-60%), and decreased mtNOS protein expression (70%). Immunohistochemistry with anti-inducible NOS antibody linked to gold particles localized mtNOS at the inner mitochondrial membranes. Histochemical right atrial NOS (NADPH-diaphorase) decreased 55% after heart denervation. The effects of autonomic denervation on the NO system were partially prevented by thyroidectomy performed simultaneously with autonomic blockade. Western blot analysis indicated a very rapid mtNOS protein turnover (half time=120 min) with a process of protein expression that was upregulated by thyroidectomy and a degradation process that was downregulated by the autonomic nervous system. The observations suggest that NO-mediated pathways contribute to pacemaker heart activity, likely through the NO steady-state levels in the right atrium and the whole heart.

Animals↗
PubMed2006

Mitochondrial metabolic states regulate nitric oxide and hydrogen peroxide diffusion to the cytosol.

Mitochondria isolated from rat heart, liver, kidney and brain (respiratory control 4.0-6.5) release NO and H2O2 at rates that depend on the mitochondrial metabolic state: releases are higher in state 4, about 1.7-2.0 times for NO and 4-16 times for H2O2, than in state 3. NO release in rat liver mitochondria showed an exponential dependence on membrane potential in the range 55 to 180 mV, as determined by Rh-123 fluorescence. A similar behavior was reported for mitochondrial H2O2 production by [S.S. Korshunov, V.P. Skulachev, A.A. Starkov, High protonic potential actuates a mechanism of production of reactive oxygen species in mitochondria. FEBS Lett. 416 (1997) 15_18.]. Transition from state 4 to state 3 of brain cortex mitochondria was associated to a decrease in NO release (50%) and in membrane potential (24-53%), this latter determined by flow cytometry and DiOC6 and JC-1 fluorescence. The fraction of cytosolic NO provided by diffusion from mitochondria was 61% in heart, 47% in liver, 30% in kidney, and 18% in brain. The data supports the speculation that NO and H2O2 report a high mitochondrial energy charge to the cytosol. Regulation of mtNOS activity by membrane potential makes mtNOS a regulable enzyme that in turn regulates mitochondrial O2 uptake and H2O2 production.

Animals↗
PubMed2006

Mitochondrial metabolic states and membrane potential modulate mtNOS activity.

The mitochondrial metabolic state regulates the rate of NO release from coupled mitochondria: NO release by heart, liver and kidney mitochondria was about 40-45% lower in state 3 (1.2, 0.7 and 0.4 nmol/min mg protein) than in state 4 (2.2, 1.3 and 0.7 nmol/min mg protein). The activity of mtNOS, responsible for NO release, appears driven by the membrane potential component and not by intramitochondrial pH of the proton motive force. The intramitochondrial concentrations of the NOS substrates, L-arginine (about 310 microM) and NADPH (1.04-1.78 mM) are 60-1000 times higher than their KM values. Moreover, the changes in their concentrations in the state 4-state 3 transition are not enough to explain the changes in NO release. Nitric oxide release was exponentially dependent on membrane potential as reported for mitochondrial H2O2 production [S.S. Korshunov, V.P. Skulachev, A.A. Satarkov, High protonic potential actuates a mechanism of production of reactive oxygen species in mitochondria. FEBS Lett. 416 (1997) 15-18.]. Agents that decrease or abolish membrane potential minimize NO release while the addition of oligomycin that produces mitochondrial hyperpolarization generates the maximal NO release. The regulation of mtNOS activity, an apparently voltage-dependent enzyme, by membrane potential is marked at the physiological range of membrane potentials.

Animals↗
PubMed2005

Vitamin E at high doses improves survival, neurological performance, and brain mitochondrial function in aging male mice.

Male mice receiving vitamin E (5.0 g alpha-tocopherol acetate/kg of food) from 28 wk of age showed a 40% increased median life span, from 61 +/- 4 wk to 85 +/- 4 wk, and 17% increased maximal life span, whereas female mice equally supplemented exhibited only 14% increased median life span. The alpha-tocopherol content of brain and liver was 2.5-times and 7-times increased in male mice, respectively. Vitamin E-supplemented male mice showed a better performance in the tight-rope (neuromuscular function) and the T-maze (exploratory activity) tests with improvements of 9-24% at 52 wk and of 28-45% at 78 wk. The rates of electron transfer in brain mitochondria, determined as state 3 oxygen uptake and as NADH-cytochrome c reductase and cytochrome oxidase activities, were 16-25% and 35-38% diminished at 52-78 wk. These losses of mitochondrial function were ameliorated by vitamin E supplementation by 37-56% and by 60-66% at the two time points considered. The activities of mitochondrial nitric oxide synthase and Mn-SOD decreased 28-67% upon aging and these effects were partially (41-68%) prevented by vitamin E treatment. Liver mitochondrial activities showed similar effects of aging and of vitamin E supplementation, although less marked. Brain mitochondrial enzymatic activities correlated negatively with the mitochondrial content of protein and lipid oxidation products (r2 = 0.58-0.99, P < 0.01), and the rates of respiration and of complex I and IV activities correlated positively (r2 = 0.74-0.80, P < 0.01) with success in the behavioral tests and with maximal life span.

Aging↗
PubMed2005

Mitochondrial function and mitochondria-induced apoptosis in an overstimulated rat ovarian cycle.

Female rats were treated with FSH (40 IU/kg) on the first and second diestrus days (D1 and D2) and with LH (40 IU/kg) on the proestrus (P) day to synchronize and maximize ovarian changes. Follicle area increased by 50% from D1 to P, and the estrus (E) phase showed multiple corpora lutea and massive apoptosis. Increased oxygen uptakes (42-102%) were determined in ovary slices and in isolated mitochondria in active state 3 along the proliferation phase (D1-D2-P) that returned to initial values in the E phase. Mitochondrial content and the electron transfer activities of complexes I and IV were also maximal in the P phase (20-79% higher than in D1). Production of NO by mitochondrial nitric oxide synthase (mtNOS), biochemically determined, and the mtNOS functional activity in regulating state 3 oxygen uptake were also maximal at P and 79-88% higher than at D1. The moderately increased rate of NO in the proliferative phase is associated with mitochondrial biogenesis, whereas the high rate of NO generation by mtNOS at phase P appears to trigger mitochondria-dependent apoptosis. The calculated fraction of ovary mitochondria in state 3 was at a minimal value at the P phase. Mitochondrial oxidative damage, with increased thiobarbituric acid-reactive substances and protein carbonyls, indicates progressive mitochondrial dysfunction between phases P and E. The roles of mitochondria as ATP provider, as a source of NO to signal for mitochondrial proliferation and mitochondria-dependent apoptosis, and as a source of O(2)(-) and H(2)O(2) appear well adapted to serve the proliferation-apoptosis sequence of the ovarian cycle.

Animals↗
PubMed2005

Effect of sustained hypobaric hypoxia during maturation and aging on rat myocardium. II. mtNOS activity.

Mitochondrial nitric oxide (NO) production was assayed in rats submitted to hypobaric hypoxia and in normoxic controls (53.8 and 101.3 kPa air pressure, respectively). Heart mitochondria from young normoxic animals produced 0.62 and 0.37 nmol NO.min(-1).mg protein(-1) in metabolic states 4 and 3, respectively. This production accounts for a release to the cytosol of 29 nmol NO.min(-1).g heart(-1) and for 55% of the NO generation. The mitochondrial NO synthase (mtNOS) activity measured in submitochondrial membranes at pH 7.4 was 0.69 nmol NO.min(-1).mg protein(-1). Rats exposed to hypobaric hypoxia for 2-18 mo showed 20-60% increased left ventricle mtNOS activity compared with their normoxic siblings. Left ventricle NADH-cytochrome-c reductase and cytochrome oxidase activities decreased by 36 and 12%, respectively, from 2 to 18 mo of age, but they were not affected by hypoxia. mtNOS upregulation in hypoxia was associated with a retardation of the decline in the mechanical activity of papillary muscle upon aging and an improved recovery after anoxia-reoxygenation. The correlation of left ventricle mtNOS activity with papillary muscle contractility (determined as developed tension, maximal rates of contraction and relaxation) showed an optimal mtNOS activity (0.69 nmol.min(-1).mg protein(-1)). Heart mtNOS activity is regulated by O(2) in the inspired air and seems to play a role in NO-mediated signaling and myocardial contractility.

Acclimatization↗
PubMed2005

Heart mitochondrial nitric oxide synthase is upregulated in male rats exposed to high altitude (4,340 m).

Male rats exposed for 21 days to high altitude (4,340 m) responded with arrest of weight gain and increased hematocrit and testosterone levels. High altitude significantly (58%) increased heart mitochondrial nitric oxide (NO) synthase (mtNOS) activity, whereas heart cytosolic endothelial NOS (eNOS) and liver mtNOS were not affected. Western blot analysis found heart mitochondria reacting only with anti-inducible NOS (iNOS) antibodies, whereas the postmitochondrial fraction reacted with anti-iNOS and anti-eNOS antibodies. In vitro-measured NOS activities allowed the estimation of cardiomyocyte capacity for NO production, a value that increased from 57% (sea level) to 79 nmol NO.min(-1).g heart(-1) (4,340 m). The contribution of mtNOS to total cell NO production increased from 62% (sea level) to 71% (4340 m). Heart mtNOS activity showed a linear relationship with hematocrit and a biphasic quadratic association with estradiol and testosterone. Multivariate analysis showed that exposure to high altitude linearly associates with hematocrit and heart mtNOS activity, and that testosterone-to-estradiol ratio and heart weight were not linearly associated with mtNOS activity. We conclude that high altitude triggers a physiological adaptive response that upregulates heart mtNOS activity and is associated in an opposed manner with the serum levels of testosterone and estradiol.

Altitude↗
PubMed2005

Hippocampal mitochondrial dysfunction with decreased mtNOS activity in prehepatic portal hypertensive rats.

Portal hypertension is a major complication of human cirrhosis that frequently leads to central nervous system dysfunction. In our study, rats with prehepatic portal hypertension developed hippocampal mitochondrial dysfunction as indicated by decreased respiratory rates, respiratory control and mitochondrial nitric oxide synthase (mtNOS) activity in mitochondria isolated from the whole hippocampus. Succinate-dependent respiratory rates decreased by 29% in controlled state 4 and by 42% in active state 3, and respiratory control diminished by 20%. Portal hypertensive rats showed a decreased mtNOS activity of 46%. Hippocampal mitochondrial dysfunction was associated with ultrastructural damage in the mitochondria of hippocampal astrocytes and endothelial cells. Swollen mitochondria, loss of cristae and rupture of outer and inner membrane was observed in astrocytes and endothelial cells of the blood-brain barrier in parallel with the ammonia gradient. It is concluded that the moderate increase in plasma ammonia that followed portal hypertension was the potential primary cause of the observed alterations.

Animals↗
PubMed2005

Functional activity of mitochondrial nitric oxide synthase.

The functional activity of mitochondrial nitric oxide synthase (mtNOS) is determined by inhibiting O2 uptake and by enhancing H2O2 production. The effect of mtNOS activity on mitochondrial O2 uptake is assayed in state 3 respiration in two limit conditions of intramitochondrial NO: at its maximal and minimal levels. The first condition is achieved by supplementation with L-arginine and superoxide dismutase (SOD), and the second by addition of an NOS inhibitor and oxyhemoglobin. The difference between state 3 O2 uptake in both conditions constitutes the mtNOS functional activity in the inhibition of cytochrome oxidase activity. The functional activity of mtNOS in enhancing mitochondrial H2O2 generation in state 4 is given by the NO inhibition of ubiquinol-cytochrome c reductase activity. Simple determinations with the oxygen electrode or the measurement of mitochondrial H2O2 production can be used to assay the effects of physiological and pharmacological treatments on mtNOS activity.

Animals↗
PubMed2004

On the mechanism and biology of cytochrome oxidase inhibition by nitric oxide.

The detailed molecular mechanism for the reversible inhibition of mitochondrial respiration by NO has puzzled investigators: The rate constants for the binding of NO and O2 to the reduced binuclear center CuB/a3 of cytochrome oxidase (COX) are similar, and NO is able to dissociate slowly from this center whereas O2 is kinetically trapped, which altogether seems to favor the complex of COX with O2 over the complex of COX with NO. Paradoxically, the inhibition of COX by NO is observed at high ratios of O2 to NO (in the 40-500 range) and is very fast (seconds or faster). In this work, we used simple mathematical models to investigate this paradox and other important biological questions concerning the inhibition of COX by NO. The results showed that all known features of the inhibition of COX by NO can be accounted for by a direct competition between NO and O2 for the reduced binuclear center CuB/a3 of COX. Besides conciliating apparently contradictory data, this work provided an explanation for the so-called excess capacity of COX by showing that the COX activity found in tissues actually is optimized to avoid an excessive inhibition of mitochondrial respiration by NO, allowing a moderate, but not excessive, overlap between the roles of NO in COX inhibition and in cellular signaling. In pathological situations such as COX-deficiency diseases and chronic inflammation, an excessive inhibition of the mitochondrial respiration is predicted.

Electron Transport Complex IV↗
PubMed2004

Mitochondrial nitric oxide metabolism in rat muscle during endotoxemia.

In this study, heart and diaphragm mitochondria produced 0.69 and 0.77 nmol nitric oxide (NO)/min mg protein, rates that account for 67 and 24% of maximal cellular NO production, respectively. Endotoxemia and septic shock occur with an exacerbated inflammatory response that damages tissue mitochondria. Skeletal muscle seems to be one of the main target organs in septic shock, showing an increased NO production and early oxidative stress. The kinetic properties of mitochondrial nitric oxide synthase (mtNOS) of heart and diaphragm were determined. For diaphragm, the KM values for O2 and L-Arg were 4.6 and 37 microM and for heart were 3.3 and 36 microM. The optimal pH for mtNOS activity was 6.5 for diaphragm and 7.0 for heart. A marked increase in mtNOS activity was observed in endotoxemic rats, 90% in diaphragm and 30% in heart. Diaphragm and heart mitochondrial O2*- and H2O2 production were 2- to 3-fold increased during endotoxemia and Mn-SOD activity showed a 2-fold increase in treated animals, whereas catalase activity was unchanged. One of the current hypotheses for the molecular mechanisms underlying the complex condition of septic shock is that the enhanced NO production by mtNOS leads to excessive peroxynitrite production and protein nitration in the mitochondrial matrix, causing mitochondrial dysfunction and contractile failure.

Animals↗