Raloxifene affects fatty acid oxidation in livers from ovariectomized rats by acting as a pro-oxidant agent.

Estrogen deficiency accelerates the development of several disorders including visceral obesity and hepatic steatosis. The predisposing factors can be exacerbated by drugs that affect hepatic lipid metabolism. The aim of the present work was to determine if raloxifene, a selective estrogen receptor modulator (SERM) used extensively by postmenopausal women, affects hepatic fatty acid oxidation pathways. Fatty acids oxidation was measured in the livers, mitochondria and peroxisomes of ovariectomized (OVX) rats. Mitochondrial and peroxisomal ß-oxidation was inhibited by raloxifene at a concentration range of 2.5-25 µM. In perfused livers, raloxifene reduced the ketogenesis from endogenous and exogenous fatty acids and increased the ß-hydroxybutyrate/acetoacetate ratio. An increase in ¹4CO2 production without a parallel increase in the oxygen consumption indicated that raloxifene caused a diversion of NADH from the mitochondrial respiratory chain to another oxidative reaction. It was found that raloxifene has a strong ability to react with H2O2 in the presence of peroxidase. It is likely that the generation of phenoxyl radical derivatives of raloxifene in intact livers led to the co-oxidation of NADH and a shift of the cellular redox state to an oxidised condition. This change can perturb other important liver metabolic processes dependent on cellular NADH/NAD⁺ ratio.

Action of quercetin on glycogen catabolism in the rat liver.

1. The influence of quercetin on glycogen catabolism and related parameters was investigated in the isolated perfused rat liver and subcellular systems. 2. Quercetin stimulated glycogenolysis (glucose release). This effect was already evident at a concentration of 50 microM maximal at 300 microM and declined at higher concentrations. Quercetin also stimulated oxygen consumption, with a similar concentration dependence. 3. Lactate production from endogenous glycogen (glycolysis) was diminished by quercetin without significant changes in pyruvate production. 4. Quercetin did not inhibit glucose transport into cells but decreased intracellular sequestration of [5-(3)H]glucose under conditions of net glucose release. 5. In isolated mitochondria, quercetin diminished the energy transduction efficiency. It also inhibited several enzymatic activities, e.g. the K(+)-ATPase/Na(+)-ATPase of plasma membrane vesicles and the glucose 6-phosphatase of isolated microsomes. 6. No significant changes of the cellular contents of AMP, ADP and ATP were found. The cellular content of glucose 6-phosphate, however, was increased (3.12-fold). 7. Some of the effects of quercetin (glycogenolysis stimulation) can be attributed to its action on mitochondrial energy metabolism, as, for example, uncoupling of oxidative phosphorylation. However, the multiplicity of the effects on several enzymatic systems certainly produces an intricate interplay that also generates complex and apparently contradictory effects.

The uncoupling effect of the nonsteroidal anti-inflammatory drug nimesulide in liver mitochondria from adjuvant-induced arthritic rats.

The aim of the present study was to evaluate the changes caused by adjuvant-induced arthritis in liver mitochondria and to investigate the effects of the nonsteroidal anti-inflammatory drug nimesulide. The main alterations observed in liver mitochondria from arthritic rats were: higher rates of state IV and state III respiration with beta-hydroxybutyrate as substrate; reduced respiratory control ratio and impaired capacity for swelling dependent on beta-hydroxybutyrate oxidation. No alterations were found in the activities of NADH oxidase and ATPase. Nimesulide produced: (1) stimulation of state IV respiration; (2) decrease in the ADP/O ratio and in the respiratory control ratio; (3) stimulation of ATPase activity of intact mitochondria; (4) inhibition of swelling driven by the oxidation of beta-hydroxybutyrate; (5) induction of passive swelling due to NH(3)/NH(4)+ redistribution. The activity of NADH oxidase was insensitive to nimesulide. Mitochondria from arthritic rats showed higher sensitivity to nimesulide regarding respiratory activity. The results of this work allow us to conclude that adjuvant-induced arthritis leads to quantitative changes in some mitochondrial functions and in the sensitivity to nimesulide. Direct evidence that nimesulide acts as an uncoupler was also presented. Since nimesulide was active in liver mitochondria at therapeutic levels, the impairment of energy metabolism could lead to disturbances in the liver responses to inflammation, a fact that should be considered in therapeutic intervention.

Effects of norepinephrine on the metabolism of fatty acids with different chain lengths in the perfused rat liver.

The effects of norepinephrine on ketogenesis in isolated hepatocytes have been reported as ranging from stimulation to inhibition. The present work was planned with the aim of clarifying these discrepancies. The experimental system was the once-through perfused liver from fasted and fed rats. Fatty acids with chain lengths varying from 8-18 were infused. The effects of norepinephrine depended on the metabolic state of the rat and on the nature of the fatty acid. Norepinephrine clearly inhibited ketogenesis from long-chain fatty acids (stearate > palmitate > oleate), but had little effect on ketogenesis from medium-chain fatty acids (octanoate and laureate). With palmitate the decrease in oxygen uptake was restricted to the substrate stimulated portion; with stearate, the decrease exceeded the substrate stimulated portion; with oleate, oxygen uptake was transiently inhibited. Withdrawal of Ca2+ attenuated the inhibitory effects. 14CO2 production from [1-14C]oleate was inhibited. Net uptake of the fatty acids was not affected by norepinephrine. In livers from fed rats, oxygen uptake and ketogenesis from stearate were only transiently inhibited. The conclusions are: (a) in the fasted state norepinephrine reduces ketogenesis and respiration by means of a Ca2+-dependent mechanism; (b) the degree of inhibition varies with the chain length and the degree of saturation of the fatty acids; (c) norepinephrine favours esterification of the activated long-chain fatty acids in detriment to oxidation; (d) in the fed state the stimulatory action of norepinephrine on glycogen catabolism induces conditions which are able to reverse inhibition of ketogenesis and oxygen uptake.

Effects of fusaric acid on rat liver mitochondria.

The effects of fusaric acid on hepatic energy metabolism were measured. Three experimental systems were employed: (a) Intact rat liver mitochondria; (b) freeze-thawing disrupted mitochondria; and (c) the isolated perfused rat liver. Fusaric acid affects mitochondrial energy metabolism by at least three modes of action: (1) Inhibition of succinate-dehydrogenase (in the 10(-3)-10(-2) M range); (2) inhibition of oxidative phosphorylation (in the 10(-5)-10(-4) M range); and (3) inhibition of alpha-ketoglutarate-dehydrogenase (in the 10(-5)-10(-4) M range). The inhibition of oxidative phosphorylation seems to be the result of a direct action on the ATP-synthase/ATPase without significant inhibition of the ATP/ADP exchange. In the isolated perfused rat liver, fusaric acid inhibits oxygen uptake and gluconeogenesis from pyruvate, the latter being strictly dependent on intramitochondrially generated ATP. The effects of fusaric acid on rat liver mitochondria are similar to those reported previously for maize root mitochondria. However, except for the action on succinate-dehydrogenase, rat liver mitochondria are approximately two orders of magnitude more sensitive than maize root mitochondria.

Effects of the nonsteroidal anti-inflammatory drug piroxicam on rat liver mitochondria.

1. The effects of piroxicam, a nonsteroidal anti-inflammatory drug, on rat liver mitochondria were investigated in order to obtain direct evidence about a possible uncoupling effect, as suggested by a previous work with the perfused rat liver. 2. Piroxicam increased respiration in the absence of exogenous ADP and decreased respiration in the presence of exogenous ADP, the ADP/O ratios and the respiratory control ratios. 3. The ATPase activity of intact mitochondria was increased by piroxicam. With 2,4-dinitrophenol uncoupled mitochondria, inhibition was observed. The ATPase activity of freeze-thawing disrupted mitochondria was insensitive to piroxicam. 4. Swelling driven by the oxidation of several substrates and safranine uptake induced by succinate oxidation were inhibited. 5. The results of this work represent a direct evidence that piroxicam acts as an uncoupler, thus, decreasing mitochondrial ATP generation.

Effects of the nonsteroidal anti-inflammatory drug piroxicam on energy metabolism in the perfused rat liver.

1. The actions of piroxicam, a nonsteroidal and noncarboxylic anti-inflammatory drug, on the metabolism of the isolated perfused rat liver were investigated. The main purpose was to verify if piroxicam is also active on glycogenolysis and energy metabolism, as demonstrated for several carboxylic nonsteroidal anti-inflammatories. 2. Piroxicam increased oxygen consumption in livers from both fed and fasted rats. 3. Piroxicam increased glucose release and glycolysis from endogenous glycogen (glycogenolysis). 4. Gluconeogenesis from lactate plus pyruvate was inhibited. 5. The action of piroxicam on oxygen consumption was blocked by antimycin A, but not by atractyloside. 6. The action of piroxicam in the perfused rat liver metabolism seems to be a consequence of its action on mitochondria. 7. It can be concluded that inhibition of energy metabolism and stimulation of glycogenolysis are not specific properties of carboxylic nonsteroidal anti-inflammatory drugs.