Animal and plant uncoupling protein (UCP) homologues form a subfamily of mitochondrial carriers that are evolutionarily related and possibly derived from a proton/anion transporter ancestor. The ...brown adipose tissue (BAT) UCP1 has a marked and strongly regulated uncoupling activity, essential to the maintenance of body temperature in small mammals. UCP homologues identified in plants are induced in a cold environment and may be involved in resistance to chilling. The biochemical activities and biological functions of the recently identified mammalian UCP2 and UCP3 are not well known. However, recent data support a role for these UCPs in State 4 respiration, respiration uncoupling and proton leaks in mitochondria. Moreover, genetic studies suggest that UCP2 and UCP3 play a part in energy expenditure in humans. The UCPs may also be involved in adaptation of cellular metabolism to an excessive supply of substrates in order to regulate the ATP level, the NAD(+)/NADH ratio and various metabolic pathways, and to contain superoxide production. A major goal will be the analysis of mice that either lack the UCP2 or UCP3 gene or overexpress these genes. Other aims will be to investigate the possible roles of UCP2 and UCP3 in response to oxidative stress, lipid peroxidation, inflammatory processes, fever and regulation of temperature in certain specific parts of the body.
Hyperosmotic conditions are associated to several pathological states. In this article, we evaluate the consequence of hyperosmotic medium on cellular energy metabolism. We demonstrate that exposure ...of cells to hyperosmotic conditions immediately reduces the mitochondrial oxidative phosphorylation rate. This causes an increase in glycolysis, which represses further respiration. This is known as the Warburg or Crabtree effect. In addition to aerobic glycolysis, we observed two other cellular responses that would help to preserve cellular ATP level and viability: A reduction in the cellular ATP turnover rate and a partial mitochondrial uncoupling which is expected to enhance ATP production by Krebs cycle. The latter is likely to constitute another metabolic adaptation to compensate for deficient oxidative phosphorylation that, importantly, is not dependent on glucose.
Cyclic fertilin peptide (cFEE: phenylalanine, glutamic acid; glutamic acid) improves gamete interaction in humans. We investigate whether it could be via improvement of sperm movement parameters and ...their mitochondrial ATP production. Sperm movement parameters were studied using computer-assisted sperm analysis (CASA) in sperm samples from 38 patients with normal sperm in medium supplemented with cyclic fertilin against a control group. Sperm mitochondrial functions were studied using donor's sperm, incubated or not with cFEE. It was evaluated by the measurement of their ATP production using bioluminescence, their respiration by high resolution oxygraphy, and of mitochondrial membrane potential (MMP) using potentiometric dyes and flow cytometry. cFEE significantly improved sperm movement parameters and percentage of hyperactivated sperm. Impact of inhibitors showed OXPHOS as the predominant energy source for sperm movement. However, cFEE had no significant impact on any of the analyzed mitochondrial bioenergetic parameters, suggesting that it could act via a more efficient use of its energy resources.
•Sulfide oxidation is evaluated in mitochondria from liver biopsies of obese patients.•Sulfide addition stimulated (<10μM) or inhibited (>10μM) mitochondrial respiration.•We generated steady states ...with balanced sulfide infusion and oxidation rates.•The maximal sulfide oxidation rate ranged from 27% to 155% of the respiratory rate.•Explanations are proposed for these high values of possible oxidation rates.
Hydrogen sulfide (H2S) is the third gasotransmitter discovered. Sulfide shares with the two others (NO and CO) the same inhibiting properties towards mitochondrial respiration. However, in contrast with NO or CO, sulfide at concentrations lower than the toxic (μM) level is an hydrogen donor and a substrate for mitochondrial respiration. This is due to the activity of a sulfide quinone reductase found in a large majority of mitochondria. An ongoing study of the metabolic state of liver in obese patients allowed us to evaluate the sulfide oxidation capacity with twelve preparations of human liver mitochondria. The results indicate relatively high rates of sulfide oxidation with a large variability between individuals. These observations made with isolated mitochondria appear in agreement with the main characteristics of sulfide oxidation as established before with the help of cellular models.
The coupling of oxygen consumption to ADP phosphorylation is incomplete, as is particularly evident in brown adipocyte mitochondria
which use a regulated uncoupling mechanism to dissipate heat ...produced by substrate oxidation. In brown adipose tissue, uncoupling
is effected by a specific protein in the inner mitochondrial membrane referred to as uncoupling protein-1 (UCP1). UCP1 gene
disruption in mice has confirmed UCP1's role in cold-induced thermogenesis. Genetic analysis of human cohorts has suggested
that UCP1 plays a minor role in the control of fat content and body weight. The recent cloning of UCP2 and UCP3, two homologues
of UCP1, has boosted research on the importance of respiration control in metabolic processes, metabolic diseases and energy
balance. UCP2 is widely expressed in different organs whereas UCP3 is mainly present in skeletal muscle. The chromosomal localization
of UCP2 as well as UCP2 mRNA induction by a lipid-rich diet in obesity-resistant mice suggested that UCP2 is involved in diet-induced
thermogenesis. A strong linkage between markers in the vicinity of human UCP2 and UCP3 (which are adjacent genes) and resting
metabolic rate was calculated. UCPs are known or supposed to participate in basal and regulatory thermogenesis, but their
exact biochemical and physiological functions have yet to be elucidated. UCPs may constitute novel targets in the development
of drugs designed to modulate substrate oxidation. However, very recent data suggest an important role for the UCPs in the
control of production of free radicals by mitochondria, and in response to oxidants.
Hydrogen sulfide (H₂S) is present in the lumen of the human large intestine at millimolar concentrations. However, the concentration of free (unbound) sulfide is in the micromolar range due to a ...large capacity of fecal components to bind the sulfide. H₂S can be produced by the intestinal microbiota from alimentary and endogenous sulfur-containing compounds including amino acids. At excessive concentration, H₂S is known to severely inhibit cytochrome c oxidase, the terminal oxidase of the mitochondrial electron transport chain, and thus mitochondrial oxygen (O₂) consumption. However, the concept that sulfide is simply a metabolic troublemaker toward colonic epithelial cells has been challenged by the discovery that micromolar concentration of H₂S is able to increase the cell respiration and to energize mitochondria allowing these cells to detoxify and to recover energy from luminal sulfide. The main product of H₂S metabolism by the colonic mucosa is thiosulfate. The enzymatic activities involved in sulfide oxidation by the colonic epithelial cells appear to be sulfide quinone oxidoreductase considered as the first and rate-limiting step followed presumably by the action of sulfur dioxygenase and rhodanese. From clinical studies with human volunteers and experimental works with rodents, it appears that H₂S can exert mostly pro- but also anti-inflammatory effects on the colonic mucosa. From the available data, it is tempting to propose that imbalance between the luminal concentration of free sulfide and the capacity of colonic epithelial cells to metabolize this compound will result in an impairment of the colonic epithelial cell O₂ consumption with consequences on the process of mucosal inflammation. In addition, endogenously produced sulfide is emerging as a prosecretory neuromodulator and as a relaxant agent toward the intestinal contractibility. Lastly, sulfide has been recently described as an agent involved in nociception in the large intestine although, depending on the experimental design, both pro- and anti-nociceptive effects have been reported.
Background: Although methylene blue (MB) had long been proposed to counteract the effects of cyanide (CN) intoxication, research on its mechanisms of action and efficacy has been abandoned for ...decades. Recent studies on the benefits of MB in post-anoxic injuries have prompted us to reexamine the relevance of this historical observation.
Methods: Our study was performed in adult male Sprague-Dawley rats and on HEK293T epithelial cells. First, the effects and toxicity of MB (0-80 mg/kg) on circulation and metabolism were established in four urethane-anesthetized rats. Then nine rats received a lethal infusion of a solution of KCN (0.75 mg/kg/min) and were treated by either saline or MB, at 20 mg/kg, a dose that we found to be innocuous in rat and to correspond to a dose of about 4 mg/kg in humans. MB was also administered 5 min after the end of a sub-lethal exposure to CN in a separate group of 10 rats. In addition, ATP/ADP ratio, ROS production, mitochondrial membrane potential (Δψm) and cellular O
2
consumption rate (OCR) were determined in HEK293T cells exposed to toxic levels of CN (200 µM for 10 min) before and after applying a solution containing MB (1-100 µM for 10 min).
Results: Methylene blue was found to be innocuous up to 50 mg/kg. KCN infusion (0.75 mg/kg/min) killed all animals within 7-8 min. MB (20 mg/kg) administered at the same time restored blood pressure, cardiac contractility and limited O
2
deficit, allowing all the animals to survive, without any significant methemoglobinemia. When administered 5 min after a non-lethal CN intoxication, MB sped up the recovery of lactate and O
2
deficit. Finally, MB was able to decrease the production of ROS and restore the ATP/ADP ratio, Δψm as well as OCR of epithelial cells intoxicated by CN.
Conclusions: The present observations should make us consider the potential interest of MB in the treatment of CN intoxication. The mechanisms of the antidotal properties of MB cannot be accounted for by the creation of a cyanomethemoglobinemia, rather its protective effects appears to be related to the unique properties of this redox dye, which, depending on the dose, could directly oppose some of the consequences of the metabolic depression produced by CN at the cellular level.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Obesity, i.e. an excess of white adipose tissue (WAT), predisposes to the development of type 2 diabetes and cardiovascular disease. Brown adipose tissue is present in rodents but not in adult ...humans. It expresses uncoupling protein 1 (UCP1) that allows dissipation of energy as heat. Peroxisome proliferator-activated receptor γ (PPARγ) and PPARγ coactivator 1α (PGC-1α) activate mouse UCP1 gene transcription. We show here that human PGC-1α induced the activation of the human UCP1 promoter by PPARγ. Adenovirus-mediated expression of human PGC-1α increased the expression of UCP1, respiratory chain proteins, and fatty acid oxidation enzymes in human subcutaneous white adipocytes. Changes in the expression of other genes were also consistent with brown adipocyte mRNA expression profile. PGC-1α increased the palmitate oxidation rate by fat cells. Human white adipocytes can therefore acquire typical features of brown fat cells. The PPARγ agonist rosiglitazone potentiated the effect of PGC-1α on UCP1 expression and fatty acid oxidation. Hence, PGC-1α is able to direct human WAT PPARγ toward a transcriptional program linked to energy dissipation. However, the response of typical white adipocyte targets to rosiglitazone treatment was not altered by PGC-1α. UCP1 mRNA induction was shown in vivo by injection of the PGC-1α adenovirus in mouse white fat. Alteration of energy balance through an increased utilization of fat in WAT may be a conceivable strategy for the treatment of obesity.
Hydrogen sulfide (H2S) is the third gasotransmitter described in mammals. These gasotransmitters (H2S, CO, and NO) are small molecules able to diffuse freely across membranes and thus susceptible to ...reach easily intracellular targets, one of which is the respiratory enzyme cytochrome oxidase subject to complete inhibition by low micromolar concentrations of these gases. However in contrast to NO or CO, H2S can be metabolized by a sulfide quinone reductase feeding the mitochondrial respiratory chain with the hydrogen atoms of sulfide. Sulfide is thus a two-sided molecule: substrate or poison according to the concentration. The aim of this chapter is to present a mean to monitor sulfide oxidation by isolated mitochondria or cells and to summarize how the properties of this amazing couple (mitochondria and sulfide) translate into practical and conceptual consequences.
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