A study is presented on the interaction of ceramide with the respiratory chain of rat heart mitochondria, and a comparison is made between the effects elicited by short- and long-chain ceramides. N-Acetylsphingosine (C(2)-ceramide) and N-palmitoylsphingosine (C(16)-ceramide) inhibited to the same extent the pyruvate+malate-dependent oxygen consumption. Succinate-supported respiration was also inhibited by ceramides, but this activity was substantially restored upon the addition of cytochrome c, which, on the contrary, was ineffective toward the ceramide-inhibited NADH-linked substrate oxidation. Direct measurements showed that short- and long-chain ceramides caused a large release of cytochrome c from mitochondria. The ceramide-dependent inhibition of pyruvate+malate and succinate oxidation caused reactive oxygen species to be produced at the level of either complex I or complex III. The activity of the cytochrome c oxidase, measured as ascorbate/TMPD oxidase activity, was significantly stimulated and inhibited by C(2)- and C(16)-ceramide, respectively. Similar effects were observed on the activity of the individual respiratory complexes isolated from bovine heart. Short- and long-chain ceramides had definitely different effects on the mitochondrial membrane potential. C(2)-ceramide caused an almost complete collapse of the respiration-dependent membrane potential, whereas C(16)-ceramide had a negligible effect. Similar results were obtained when the potential was generated in liposome-reconstituted complex III respiring at the steady-state. Furthermore, C(2)-ceramide caused a drop of the membrane potential generated by ATP hydrolysis instead of respiration, whereas C(16)-ceramide did not. Finally, only short-chain ceramides inhibited markedly the reactive oxygen species generation associated with membrane potential-dependent reverse electron flow from succinate to complex I. The emerging indication is that the short-chain ceramide-dependent collapse of membrane potential is a consequence of their ability to perturb the membrane structure, leading to an unspecific increase of its permeability.

No abstract

No abstract

Long chain free fatty acids (FFA) exert, according to their actual concentration, different effects on the energy conserving system of mitochondria. Sub-micromolar concentrations of arachidonic acid (AA) rescue DeltapH-dependent depression of the proton pumping activity of the bc1 complex. This effect appears to be due to a direct interaction of AA with the proton-input mouth of the pump. At micromolar concentrations FFA increase the proton conductance of the inner membrane acting as protonophores. FFA can act as natural uncouplers, causing a mild uncoupling, which prevents reactive oxygen species production in the respiratory resting state. When Ca(2+)-loaded mitochondria are exposed to micromolar concentrations of FFA, the permeability of the inner membrane increases, resulting in matrix swelling, rupture of the outer membrane and release of intermembrane pro-apoptotic proteins. The characteristics of AA-induced swelling appear markedly different in mitochondria isolated from heart or liver. While in the latter it presents the canonical features of the classical permeability transition (PT), in heart mitochondria substantial differences are observed concerning CsA sensitivity, DeltaPsi dependence, reversibility by BSA and specificity for the activating divalent cation. In heart mitochondria, the AA-dependent increase of the inner membrane permeability is affected by ANT ligands such as adenine nucleotides and atractyloside. AA apparently causes a Ca2+-mediated conversion of ANT from a translocator to a channel system. Upon diamide treatment of heart mitochondria, the Ca2+/AA-induced CsA insensitive channel is converted into the classical PT pore. The relevance of these observations in terms of tissue-specific components of the putative PTP and heart ischemic and post-ischemic process is discussed.

Dendritic cells (DC) are potent antigen-presenting cells capable of inducing T and B responses and immune tolerance. We have characterized some aspects of energy metabolism accompanying the differentiation process of human monocytes into DC. Compared to precursor monocytes, DC exhibited a much larger number of mitochondria and consistently (i) a higher endogenous respiratory activity and (ii) a more than sixfold increase in ATP content and an even larger increase in the activity of the mitochondrial marker enzyme citrate synthase. The presence in the culture medium of rotenone, an inhibitor of the respiratory chain Complex I, prevented the increase in mitochondrial number and ATP level, without affecting cell viability. Rotenone inhibited DC differentiation, as revealed by the observation that the expression of CD1a, which is a specific surface marker of DC differentiation, was strongly reduced. Cells cultured in the presence of rotenone displayed a lower content of growth factor-induced, mitochondrially generated, hydrogen peroxide. A similar drop in ROS was observed upon addition of catalase, which caused functional effects similar to those produced by rotenone treatment. These results suggest that ROS play a crucial role in DC differentiation and that mitochondria are an important source of ROS in this process. © 2008 Elsevier Inc. All rights reserved.Keywords: Dendritic cells; Mitochondria; Reactive oxygen species; Oxidative phosphorylation; Free radicals Effective immune responses require correct localization and functioning of dendritic cells (DC). Dendritic cells are the most potent and versatile antigen-presenting cells, with a unique ability to induce specific immune responses as well as tolerance [1,2]. In peripheral tissues they reside in an immature state waiting for incoming antigens. After capturing and processing the antigens, DC undergo a maturation process which culminates in dramatic changes in functions and migratory properties [3,4]. The localization of mature DC to the draining lymph nodes coincides with the presentation of processed antigens to naïve T cells, triggering the initiation of specific immune responses [2,5]. An in vitro method to differentiate immature DC from CD14 + monocyte precursors cultured in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) is very well established [6,7].Reactive oxygen species (ROS) have been identified as important second messengers involved in the transduction of several signaling pathways [8,9], gene expression, and cell proliferation [10]. Furthermore, recent studies have shown that growth factors, through the actions of their specific receptors, are able to increase

A study is presented of the effect of Zn2+ on the enzymatic properties of the bovine-heart cytochrome-bc, complex. Micromolar concentrations of Zn2+ reversibly inhibit the cytochrome-c reductase activity of either the cholate-solubilized or liposome-reconstituted complex. Kinetic analysis of the redox reactions of the cytochromes indicate that Zn2+ affects the activity of the complex at the quinol oxidation site. The following have been determined: (a) Zn2 + inhibits the pre-steady-state reduction of cytochrome c1 by duroquinol either in the absence or in the presence of antimycin, (b) it does not inhibit the reduction of b cytochromes in the absence of antimycin or in the presence of myxothiazol, (c) it inhibits cytochrome-b reduction in the presence of antimycin. Furthermore Zn2 + inhibits the antimycin-promoted oxidant-induced extrareduction of b cytochromes.Addition of Zn2+ to reduced bel complex causes a red shift in the absorption spectrum of cytochrome bs66 and a substantial decrease in the signal intensity of the EPR spectrum of the Fe-S protein. This is interpreted as an interaction of Zn2+ with the 2Fe-2s-cluster region of the Fe-S protein, thus giving rise to inhibition of the reductase activity and of the antimycin-insensitive reduction route of h cytochromes.A Scatchard-plot of 65Zn2+ binding to the native isolated complex gave a straight line from which a value of three binding sites and a single dissociation constant of 3 x M can be calculated, which is practically equal to the concentration causing 50% inhibition of electron flow.Zinc is an oligoelement which has been shown to have a role in the activity of more than 200 enzyme proteins. Its role can be structural, catalytic and/or regulatory [I]. As far as the respiratory complexes are concerned, several reports have indicated that Zn2+ is associated, together with other nonredox metals, with the mitochondrial-cytochrome oxidase [2-41. It is, however, questioned whether the ion plays a structural role [2, 51 or is adventitious [6]. Zn2+ selective removal was reported to cause either no change [6] or inhibition of steady-state activity of the oxidase [5, 71. In the bacterial quinol-oxidase c y t~c h r o m e -b~~~-o complex, purified from cells in the early exponential phase of aerobic growth, Zn2+ causes extensive inhibition of the quinol-oxidase activity [S]. The corresponding cytochromebc, segment of the mitochondrial-respiratory chain was shown by Skulachev et al. [9] to be inhibited by micromolar concentrations of Zn2+. Subsequently Kleiner and Von Jagow [lo], and Kleiner [ll] provided evidence for the location of the Zn2+-binding site between ubiquinone and b cytochromes. Since then much knowledge has been acquired regarding the polypeptide composition and the pathways of electron flow and proton translocation in the bel complex. Models explaining the enzymatic reactions of the be, complex have then been put forward (for review see . In this paper a study is presented of the effect of Zn2+ on the properties of the redox centers and on elec...

As a staple food, bread digestibility deserves a marked nutritional interest. Combining wide-spectrum characterization of breads, in vitro nutritional indices, and in vivo postprandial markers of gastrointestinal function, we aimed at comparing the digestibility of sourdough and baker’s yeast breads. Microbiological and biochemical data showed the representativeness of the baker´s yeast bread (BYB) and the two sourdough breads (SB and t-SB, mainly differing for the time of fermentation) manufactured at semi-industrial level. All in vitro nutritional indices had the highest scores for sourdough breads. Thirty-six healthy volunteers underwent an in vivo challenge in response to bread ingestion, while monitoring gallbladder, stomach, and oro-cecal motility. SB, made with moderate sourdough acidification, stimulated more appetite and induced lower satiety. t-SB, having the most intense acidic taste, induced the highest fullness perception in the shortest time. Gallbladder response did not differ among breads, while gastric emptying was faster with sourdough breads. Oro-cecal transit was prolonged for BYB and faster for sourdough breads, especially when made with traditional and long-time fermentation (t-SB), whose transit lasted ca. 20 min less than BYB. Differences in carbohydrate digestibility and absorption determined different post-prandial glycaemia responses. Sourdough breads had the lowest values. After ingesting sourdough breads, which had a concentration of total free amino acids markedly higher than that of BYB, the levels in blood plasma were maintained at constantly high levels for extended time.

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. b s t r a c tDendritic cells (DC) are sentinels of the immune system deriving from circulating monocyte precursors recruited to sites of inflammation. In a previous report (Del Prete et al., 2008) we showed that, after differentiation, DC exhibited increased number of condensed mitochondria and dynamic changes in their energy metabolism. A study is presented here showing that the DC differentiation process is characterized by increased expression level and activity of mitochondrial respiratory complexes, as well as by an increased mitochondrial DNA (mtDNA) copy number. Moreover, DC are equipped with more efficient antioxidant protection systems, over expressed most likely to detoxify increased ROS production, as a consequence of the much higher mitochondrial activity. Kinetic analysis of the three main mitochondrial biogenesis-associated genes revealed that the peak in PPAR␥ coactivator-1alpha (PGC-1␣) gene expression was suddenly reached few hours after the onset of the differentiation. While PGC-1␣ expression rapidly declines, the mitochondrial transcription factor A (TFAM) and nuclear respiratory factor-1 (NRF-1) expression gradually increased. These findings demonstrate that an active mitochondrial biogenesis occurs during DC differentiation and further suggest that an early input by the master regulator of mitochondrial biogenesis PGC-1␣ is needed to trigger the subsequent activation of the downstream transcription factors, NRF-1 and TFAM in this process.