Sulfide, the first inorganic substrate for human cells.

Hydrogen sulfide (H2S) is produced inside the intestine and is known as a poison that inhibits cellular respiration at the level of cytochrome oxidase. However, sulfide is used as an energetic substrate by many photo- and chemoautotrophic bacteria and by animals such as the lugworm Arenicola marina. The concentrations of sulfide present in their habitats are comparable with those present in the human colon. Using permeabilized colonic cells to which sulfide was added by an infusion pump we show that the maximal respiratory rate of colonocyte mitochondria in presence of sulfide compares with that obtained with succinate or L-alpha-glycerophosphate. This oxidation is accompanied by mitochondrial energization. In contrast, other cell types not naturally exposed to high concentration of sulfide showed much lower oxidation rates. Mitochondria showed a very high affinity for sulfide that permits its use as an energetic substrate at low micromolar concentrations, hence, below the toxic level. However, if the supply of sulfide exceeds the oxidation rate, poisoning renders mitochondria inefficient and our data suggest that an anaerobic mechanism involving partial reversion of Krebs cycle already known in invertebrates takes place. In conclusion, this work provides additional and compelling evidence that sulfide is not only a toxic compound. According to our study, sulfide appears to be the first inorganic substrate for mammalian cells characterized thus far.

Long term treatment with olanzapine mixed with the food in male rats induces body fat deposition with no increase in body weight and no thermogenic alteration.

Body weight gain is a worrying side effect of many new antipsychotic drugs. The mechanisms by which antipsychotic drugs increase weight in humans are not known. Attempts to model the metabolic effects of antipsychotic drugs in the animal have not been successful. Female rats appear to be sensitive to the effects of antipsychotics, but male rats less, and this does not match the clinical situation in humans. In previous rodent studies, antipsychotics were always given by daily gavage or injections. Antipsychotics have different pharmacokinetics in rodents and humans, and in the present study, we tested the hypothesis that the insensitivity of male rats to the effects of antipsychotics could be related to their mode of administration. Thus, we administered antipsychotic drugs mixed with the food. Animals were treated during 6 weeks with haloperidol (1mg/kg), olanzapine (1mg/kg), ziprasidone (10mg/kg), or a control solution. Animals were allowed to self-select food among three macronutrients (carbohydrates, lipids and proteins). Food selection was measured throughout the study. At the end of the study, body composition was measured by dissection and weighing of the rat's main organs and tissues. Mitochondrial thermogenesis was measured in brown adipose tissue in olanzapine-treated animals. Circulating leptin, insulin, glucose, triglycerides, cholesterol, high-density lipoprotein (HDL) were also assayed at the end of the study. The results show that none of the antipsychotic treatments modified caloric intake, food selection or body weight. Olanzapine did not alter mitochondrial thermogenesis. However, haloperidol and olanzapine induced a significant increase in adiposity and circulating leptin. Ziprasidone produced a moderate fat accumulation. It is concluded that mixing antipsychotic treatments with the food provides a reliable animal model of antipsychotic-induced fat accumulation.

Comparison of energy balance in two inbred strains of rats: Fischer F344 prone to obesity and Lou rats resistant to obesity.

This study aimed to compare energy balance, metabolic profiles and body composition between two inbred strains of rats (F344 and Lou) submitted to a self-selecting macronutrient. During the 3 weeks of experiment, the two strains did not differ significantly for their total energy intake; males: F344 = 5875.4 +/- 171.4 kJ, Lou = 5619.2 +/- 349.4 kJ; and females: F344 = 4058.8 +/- 118.7 kJ, Lou = 3864.4+/-166.4 kJ. However, F344 rats showed a higher weight gain, and percentage of total fat tissue, together with a lower percentage of carcass weight than Lou rats regardless of sex. The percentages of each macronutrient revealed a lower preference of protein for F344 males and the opposite in females for CHO. The thermogenic activity measured in interscapular brown adipose tissue was lower in Fischer than in Lou while the reverse was observed for leptinemia and insulinemia. These results indicate that the mechanism responsible for the regulation of body composition observed in Lou rats takes place very early in life and attest the interest in this strain for studying the features of resistance to obesity.

Adaptative metabolic response of human colonic epithelial cells to the adverse effects of the luminal compound sulfide.

Hydrogen sulfide (H(2)S), a bacterial metabolite present in the lumen of the large intestine, is able to exert deleterious effects on the colonic epithelium. The mechanisms involved are still poorly understood, the reported effect of sulfide being its capacity to reduce n-butyrate beta-oxidation in colonocytes. In this work, we studied both the acute effect of the sodium salt of H(2)S on human colonic epithelial cell metabolism and the adaptative response of these cells to the pre-treatment with this agent. Using the human colon carcinoma epithelial HT-29 Glc(-/+) cell model, we found that the acute effect of millimolar concentrations of NaHS was to inhibit l-glutamine, n-butyrate and acetate oxidation in a dose-dependent manner. Using micromolar concentrations of NaHS, a comparable effect but largely reversible was observed for O(2) consumption and cytochrome c oxidase activity. Pre-treatment with 1 mM NaHS induced several adaptative responses. Firstly, increased lactate release and decreased cellular oxygen consumption evidenced a Pasteur-like effect which only partly compensated for the altered mitochondrial ATP production. Thus, a decrease in the proliferation rate with a constant adenylate charge was observed. Secondly, in these pre-treated cells, NaHS induced a hypoxia-like effect on cytochrome c oxidase subunits I and II which were decreased. Thirdly, a mild uncoupling of mitochondrial respiration possibly resulting from an increase of UCP 2 protein was observed. The NaHS antimitotic activity was not due to cellular apoptosis and/or necrosis but to a proportional slowdown in all cell cycle phases. These results are compatible with a metabolic adaptative response of the HT-29 colonic epithelial cells to sulfide-induced O(2) consumption reduction which, through the maintenance of a constant energetic load and an increased mitochondrial proton leak, would participate in the preservation of cellular viability.

Intraperitoneal leptin modifies macronutrient choice in self-selecting rats.

This study aimed to evaluate the consequences on food intake and body weight (BW) of leptin administration in rats receiving a choice between the three macronutrients. Two studies were performed: during the first, rats received an acute intraperitoneal (IP) leptin administration (1 mg/kg) twice (at 8 and 14 weeks of age), at the beginning of the nocturnal cycle, while during the second, they received a chronic leptin infusion (osmotic minipump, 7 days). The total 24-h food intake after acute leptin injections was reduced by 14% and 17%, respectively. Body weight gain (BWG) after leptin injections was about half that seen on control days. Chronic leptin infusion reduced total intake, affecting mainly protein (P). Fat intake increased slightly since day 2 and became significant on the fourth day. After the leptin infusion, carbohydrate (CHO) eaters (>35% carbohydrate/total energy) significantly reduced the carbohydrate proportion in their total energy intake. There was no difference concerning macronutrient selection by fat eaters (Hfat). Leptin infusion reduced the number of mixed meals on the first day. In addition, the thermogenesis of brown adipose tissue (BAT) was higher in leptin than in control (C) rats. Consequently, leptin injections reduced food intake and BWG and increased thermogenesis, thus acting on the two terms of the energy balance. Moreover, leptin has different effects on macronutrient preferences, dependent upon age (tests 1 and 2) and the type (acute or chronic) of injection. High leptinemia level related to age or to minipump infusion lead to leptin resistance as found in old or obese subjects. It could explain our results.

High level of uncoupling protein 1 expression in muscle of transgenic mice selectively affects muscles at rest and decreases their IIb fiber content.

The mitochondrial uncoupling protein of brown adipose tissue (UCP1) was expressed in skeletal muscle and heart of transgenic mice at levels comparable with the amount found in brown adipose tissue mitochondria. These transgenic mice have a lower body weight, and when related to body weight, food intake and energy expenditure are increased. A specific reduction of muscle mass was observed but varied according to the contractile activity of muscles. Heart and soleus muscle are unaffected, indicating that muscles undergoing regular contractions, and therefore with a continuous mitochondrial ATP production, are protected. In contrast, the gastrocnemius and plantaris muscles showed a severely reduced mass and a fast to slow shift in fiber types promoting mainly IIa and IIx fibers at the expense of fastest and glycolytic type IIb fibers. These observations are interpreted as a consequence of the strong potential dependence of the UCP1 protonophoric activity, which ensures a negligible proton leak at the membrane potential observed when mitochondrial ATP production is intense. Therefore UCP1 is not deleterious for an intense mitochondrial ATP production and this explains the tolerance of the heart to a high expression level of UCP1. In muscles at rest, where ATP production is low, the rise in membrane potential enhances UCP1 activity. The proton return through UCP1 mimics the effect of a sustained ATP production, permanently lowering mitochondrial membrane potential. This very likely constitutes the origin of the signal leading to the transition in fiber types at rest.

No evidence for a basal, retinoic, or superoxide-induced uncoupling activity of the uncoupling protein 2 present in spleen or lung mitochondria.

The phenotypes observed in mice whose uncoupling protein (Ucp2) gene had been invalidated by homologous recombination (Ucp2(-/-) mice) are consistent with an increase in mitochondrial membrane potential in macrophages and pancreatic beta cells. This could support an uncoupling (proton transport) activity of UCP2 in the inner mitochondrial membrane in vivo. We used mitochondria from lung or spleen, the two organs expressing the highest level of UCP2, to compare the proton leak of the mitochondrial inner membrane of wild-type and Ucp2(-/-) mice. No difference was observed under basal conditions. Previous reports have concluded that retinoic acid and superoxide activate proton transport by UCP2. Spleen mitochondria showed a higher sensitivity to retinoic acid than liver mitochondria, but this was not caused by UCP2. In contrast with a previous report, superoxide failed to increase the proton leak rate in kidney mitochondria, where no UCP2 expression was detected, and also in spleen mitochondria, which does not support stimulation of UCP2 uncoupling activity by superoxide. Finally, no increase in the ATP/ADP ratio was observed in spleen or lung of Ucp2(-/-) mice. Therefore, no evidence could be gathered for the uncoupling activity of the UCP2 present in spleen or lung mitochondria. Although this may be explained by difficulties with isolated mitochondria, it may also indicate that UCP2 has another physiological significance in spleen and lung.