Aline Amérand

Effects of mild induced hypothermia during experimental sepsis.

Objectives:The potential advantages of lowering core temperature during sepsis are to lower energy requirement and to activate various cell-protecting pathways. We experimentally investigated whether postconditioning temperature modifications influence survival duration during experimental sepsis. Design:A prospective, randomized, experimental animal study. Setting:University laboratory. Subjects:Eighteen male Sprague-Dawley rats (median 326 g, range 310–347 g). Interventions:After anesthesia, experimental sepsis was induced by cecal ligation and perforation. The animals were subsequently assigned a core temperature range: normothermia (37°C), hyperthermia (42°C), and mild hypothermia (32°C). Anesthesia and analgesia were continuously maintained until death. Measurements and Main Results:Plasma lactate and pyruvate concentrations were measured at sepsis induction (H0), 4 hrs later (H4), and/or at the time of death. A significant increase in lactate concentration was observed at the time of death in the 42°C group (p = .04). Lactate-to-pyruvate ratio increased in the 32°C (at H4) and 42°C (at the time of death) groups (p = .04). A linear correlation between a longer survival duration and a lower assigned core temperature was observed (from 61 ± 10 mins at 42°C to 289 ± 17 mins at 37°C and to 533 ± 69 mins at 32°C; R2 = .959, p < .0001). Conclusions:The current results demonstrate that postconditioning hypothermia was associated with increased survival duration during experimental sepsis. Whether the observed benefits on survival duration are due to potential impacts on energy metabolism or to an anti-inflammatory effect of hypothermia requires further investigation.

Effect of exercise training on respiration and reactive oxygen species metabolism in eel red muscle

This paper deals with the effects of exercise training on oxygen consumption (MO(2)) and ROS metabolism in the red muscle of trained and untrained female silver eels. Their critical swimming speed (U(crit)) was determined before and after a 4-day training (10h of swimming at 70% of U(crit) and 14 h at 50%, every day). The U(crit) of trained eels increased significantly (by about 7%). The in vitro MO(2) and ROS production by the red fibres were higher (not significant) in trained than in untrained eels, but the ROS production/MO(2) ratio was alike in both groups. The antioxidant-enzyme activities and lipoperoxidation index in trained eels were both lower than those of the untrained ones. These biochemical changes related to the increase in U(crit) suggest that such a training session could maintained or even increased aerobic power of the red muscle without deleterious impact by ROS. These regulations could play a role in the eels swimming performance efficiency.

In vitro effect of hydrostatic pressure exposure on hydroxyl radical production in fish red muscle

Abstract The effects of hydrostatic pressure on reactive oxygen species (ROS) production have been studied in vitro on fish red muscle fibres. In the eel, Anguilla anguilla, previous studies have shown that hydrostatic pressure acclimatization improves oxidative phosphorylation efficiency together with a supposed concomitant decrease in electron leak and ROS production. In order to test the hypothesis of an electron leak decrease under pressure, hydroxyl radical (HO•) production and oxygen consumption were measured on fish red muscle fibres directly exposed to hydrostatic pressure. Experiments were performed under two conditions – atmospheric pressure and hydrostatic pressure (16.1 MPa) – on eel and trout (which exhibit low- and high-pressure sensitivity, respectively). This work has permitted, first, the validation of an indirect HO• measurement (in vitro) on fish red muscle and the documentation of reference values for fish. Second, at atmospheric pressure, results show higher oxygen consumption for trout (+40%) than for eel which is accompanied by higher HO• production (+90%); in addition, both species present a positive relationship between HO• production and oxygen consumption. Hydrostatic pressure exposure reverses this relationship for eel but not for trout. These preliminary results only partially verify the proposed hypothesis and further experiments are needed.

Is the silvering process similar to the effects of pressure acclimatization on yellow eels

To reproduce eels need to migrate over 6000 km and at pressure but before this migration they metamorphose into silver eels (silvering). The question raised in this study is to determine whether and how the silvering process contributes to pressure resistance. As migration represents a long swimming activity mainly performed with slow muscles, the red muscle energetics of pressure exposed silver eels was studied. By comparing these results to what has already been shown in yellow eels, we point out that the effects of the silvering process on pressure resistance are similar to the effects of pressure acclimatization in yellow eels. As previously shown, success of pressure acclimatization depends on membrane fluidity, but we raise the hypothesis that the high-pressure resistance of silver eels is due to more fluid membranes.

Effect of induced mild hypothermia on two pro-inflammatory cytokines and oxidative parameters during experimental acute sepsis

Abstract This study aimed to determine the effect of induced mild hypothermia (34°C) on the production of two cytokines (interleukin (IL-6) and tumor necrosis factor (TNF)alpha) and reactive nitrogen and oxygen species in plasma and the heart of acutely septic rats. After anesthesia and in conditions of normothermia (38°C) or mild hypothermia (34°C), acute sepsis was induced by cecal ligation and perforation. For each temperature three groups were formed: (1) baseline (blood sample collected at T0 hour), (2) sham (blood sample at T4 hours) and (3) septic (blood sample at T4 hours). At either temperature sepsis induced a significant increase in plasma IL-6, TNF-alpha and HO• concentration, compared with the sham groups (P ≤ 0.016). Compared with the normothermic septic group, septic rats exposed to mild hypothermia showed a mild decrease in TNF-alpha concentration (104 ± 50 pg/ml vs. 215 ± 114 pg/ml; P > 0.05) and a significant decrease in IL-6 (1131 ± 402 pg/ml vs. 2494 ± 691 pg/ml, P = 0.038). At either temperature sepsis induced no enhancement within the heart of lipoperoxidation (malondialdehyde content) or antioxidant activities (superoxide dismutase and catalase). In conclusion, during acute sepsis, induced mild hypothermia appears to reduce some pro-inflammatory and oxidative responses. This may, in part, explain the beneficial effect of hypothermia on survival duration of septic rats.

Effect of exercise training on oxidative stress and mitochondrial function in rat heart and gastrocnemius muscle

Abstract Objective This study aimed to explore the effect of endurance training on oxidative parameters and mitochondrial function in gastrocnemius and heart muscle. Methods Male Wistar rats were trained by running for 6 weeks. In vitro measurements of the rates of hydroxyl radical (•OH) production, oxygen consumption (in either the absence, basal rate (V0), or the presence, maximal rate (Vmax), of adenosine diphosphate), and adenosine triphosphate (ATP) production were made simultaneously in permeabilized fibers. The mitochondrial function was explored after exposure or non-exposure to an in vitro generator system of reactive oxygen species (ROS). Results Vmax was not affected by training, but V0 decreased. In conditions of maximal mitochondrial functioning, an increase in ATP rate and a decrease in •OH production occurred simultaneously. In vitro ROS exposure disturbed mitochondrial function, but training modified the vulnerability of Vmax and ATP rate to ROS in different ways. Discussion We hypothesize that the part of Vmax devoted to proton leakage was decreased in trained rats, consequently improving ATP synthesis. The data suggest that, after training, there is more efficient use of electrons in respiratory chain energy production, rather than a greater ROS scavenging capacity.

In vitro aerobic and anaerobic muscle capacities in the European eel, Anguilla anguilla: effects of a swimming session.

In order to have a general view of metabolic requirements during swimming, in vitro aerobic and anaerobic fluxes were measured in red and white muscles from silver eels and yellow eels which differ in activity levels and nutritional states. These measurements were performed in control eels and after a 4 day swimming session (70% U(crit) in yellow eels, 80% U(crit) in silver eels). A swimming session significantly increases U(crit) from 12% to 18%, depending on the stage, with a significantly higher in vitro energy cost during the yellow stage at the muscle level. In vitro, the swimming session brings about a gain in anaerobic capacities rather than in aerobic ones. Some in vivo hypotheses are proposed.

Silvering and swimming effects on aerobic metabolism and reactive oxygen species in the European eel

Silvering, the last metamorphosis in the eel life cycle induces morphological and physiological modifications in yellow eels (sedentary stage). It pre-adapts them to cope with the extreme conditions they will encounter during their 6000-km spawning migration. A previous study showed that silver eels are able to cope with reactive oxygen species (ROS) over-production linked to an increase in aerobic metabolism during sustained swimming, but the question remains as to whether this mechanism is associated with silvering. A sustained swimming session decreased red muscle in vitro mitochondrial oxygen consumption (MO2) but increased ROS production in both eel stages. The swimming exercise used here was perhaps too intense to induce a stimulation of mitochondrial function or biogenesis even when antioxidant enzyme activities were unchanged. Pro-oxidant/antioxidant imbalance by lipid peroxidation increased in yellow but significantly decreased in silver eels. The silvering process therefore appears to allow a pre-adaptation of red muscle radical metabolism to the demands of spawning migration.

Gender-dependent differences of mitochondrial function and oxidative stress in rat skeletal muscle at rest and after exercise training

ABSTRACT Objective: This study investigated gender-dependent differences of mitochondrial function and sensitivity to in vitro ROS exposure in rat skeletal muscle at rest and after exercise training. Methods: Wistar rats underwent running training for 6 weeks. In vitro measurements of hydroxyl radical production, oxygen consumption (under basal and maximal respiration conditions) and ATP production were made on permeabilized fibers. Mitochondrial function was examined after exposure and non-exposure to an in vitro generator system of reactive oxygen species (ROS). Antioxidant enzyme activities and malondialdehyde (MDA) content were also determined. Results: Compared with sedentary males, females showed a greater resistance of mitochondrial function (oxygen consumption and ATP production) to ROS exposure, and lower MDA content and antioxidant enzyme activities. The training protocol had more beneficial effects in males than females with regard to ROS production and oxidative stress. In contrast to male rats, the susceptibility of mitochondrial function to ROS exposure in trained females was unchanged. Discussion: Exercise training improves mitochondrial function oxidative capacities in both male and female rats, but is more pronounced in males as a result of different mechanisms. The resistance of mitochondrial function to in vitro oxidative stress exposure and the antioxidant responses are gender- and training-dependent, and may be related to the protective effects of estrogen.

Long-term atorvastatin treatment decreases heart maximal oxygen consumption and its vulnerability to in vitro oxidative stress in Watanabe heritable hyperlipidemic rabbit

Statins are currently used in prevention of cardiovascular diseases in high-risk populations, and could be considered in primary prevention. However, few studies are available on the long-term effects of low doses of statins, especially on mitochondrial function and reactive oxygen species (ROS) metabolism at cardiac level. This study aimed to determine potential effects of a long-term atorvastatin treatment, at low-dose concentration, on the myocardium mitochondrial respiration. Thirty-four Watanabe rabbits were treated or not with atorvastatin (2.5 mg·kg-1·day-1) from the age of 3 to 12 months. Every 3 months, proton leak, basal (V0), and maximal (Vmax) mitochondrial respiration on cardiac permeabilized fibers were measured. Additionally, the vulnerability to ROS, cardiac enzymatic antioxidant defenses, and oxidative damage (lipoperoxidation) were analyzed. Proton leak increased over the duration of the experiment (up to 60% from Vmax at 12 months). Moreover, the statin treatment induced a decrease of Vmax and a decrease of ROS susceptibility of cardiac mitochondria. However, the lipoperoxidation and the antioxidant defenses were not dependent on the presence of statin treatment, or on its duration. This is the first study showing a protective effect of long-term statins treatment against the ROS susceptibility in the cardiac muscle.