Andrea Luiza de Oliveira

Oxidative state of the liver of rats with adjuvant-induced arthritis.

Adjuvant-induced arthritis is an experimental immunopathology in rats that is often used as a model for studying autoimmune chronic inflammation and inflammatory cachexia. In these animals oxidative stress is quite pronounced in the articular inflammation sites. The purpose of this study was to evaluate oxidative stress in the liver of arthritic rats in which morphological and metabolic alterations have been reported to occur. Oxidative injury parameters, levels and production of reactive oxygen species (ROS), and antioxidant parameters were measured in the total liver homogenate and in subcellular fractions, namely cytosol, mitochondria, and peroxisomes. Arthritic rats presented higher levels of ROS than controls in the total homogenate (46% higher) and in all subcellular fractions (51, 38, and 55% higher for mitochondria, peroxisome, and cytosol, respectively). Arthritic rats also presented higher levels of protein carbonyl groups in the total homogenate (75%) and in all subcellular fractions (189, 227, and 260%, respectively, for mitochondria, peroxisomes, and cytosol). The TBARS levels of arthritic rats were more elevated in the total homogenate (36%), mitochondria (20%), and peroxisomes (16%). Arthritic rats also presented higher levels of NO markers in the peroxisomes (112%) and in the cytosol (35%). The catalase activity of all cell compartments was strongly diminished (between 77 and 87%) by arthritis, and glutathione peroxidase activities were diminished in the mitochondria (33.7%) and cytosol (41%). The cytosolic glucose-6-phosphate dehydrogenase activity, on the other hand, was increased (62.9%), the same happening with inducible peroxisomal NO synthase (119.3%). The superoxide dismutase and glutathione reductase activities were not affected. The GSH content was diminished by arthritis in all cellular compartments (50 to 59% diminution). The results reveal that the liver of rats with adjuvant-induced arthritis presents a pronounced oxidative stress and that, in consequence, injury to lipids and proteins is highly significant. The higher ROS content of the liver of arthritic rats seems to be the consequence of both a stimulated pro-oxidant system and a deficient antioxidant defense with a predominance of the latter as indicated by the strongly diminished activities of catalase and glutathione peroxidase.

Effects of Citrus aurantium (Bitter Orange) Fruit Extracts and p-Synephrine on Metabolic Fluxes in the Rat Liver

The fruit extracts of Citrus aurantium (bitter orange) are traditionally used as weight-loss products and as appetite supressants. An important fruit component is p-synephrine, which is structurally similar to the adrenergic agents. Weight-loss and adrenergic actions are always related to metabolic changes and this work was designed to investigate a possible action of the C. aurantium extract on liver metabolism. The isolated perfused rat liver was used to measure catabolic and anabolic pathways, including oxygen uptake and perfusion pressure. The C. aurantium extract and p-synephrine increased glycogenolysis, glycolysis, oxygen uptake and perfusion pressure. These changes were partly sensitive to α- and β-adrenergic antagonists. p-Synephrine (200 μM) produced an increase in glucose output that was only 15% smaller than the increment caused by the extract containing 196 μM p-synephrine. At low concentrations the C. aurantium extract tended to increase gluconeogenesis, but at high concentrations it was inhibitory, opposite to what happened with p-synephrine. The action of the C. aurantium extract on liver metabolism is similar to the well known actions of adrenergic agents and can be partly attributed to its content in p-synephrine. Many of these actions are catabolic and compatible with the weight-loss effects usually attributed to C. aurantium.

Harmful effects of usnic acid on hepatic metabolism.

Usnic acid is a naturally occurring dibenzofuran derivative found in several lichen species. The compound has been marketed as an ingredient of food supplements for weight reduction. There is evidence that the compound acts as an uncoupler of mitochondrial oxidative phosphorylation and it is also clear that consumption of the drug can lead to severe hepatotoxicity depending on the doses. Based on these and other ideas the objective of the present work was to investigate the possible effects of usnic acid on liver metabolism. Livers of male Wistar rats were perfused in a non-recirculating system. Usnic acid stimulated oxygen consumption at low concentrations, diminished the cellular ATP levels, increased the cytosolic but diminished the mitochondrial NADH/NAD(+) ratio, strongly inhibited gluconeogenesis from three different substrates (IC(50) between 1.33 and 3.61 μM), stimulated glycolysis, fructolysis, glycogenolysis and ammoniagenesis and inhibited ureogenesis. The (14)CO(2) production from [1-(14)C]octanoate and [1-(14)C]oleate was increased by usnic acid, but ketogenesis from octanoate was diminished and that from oleate was not affected. It may be concluded that the effects of usnic acid up to 2.5 μM reflect predominantly its activity as an uncoupler. At higher concentrations, however, several other effects may become significant, including inhibition of mitochondrial electron flow and inhibition of medium-chain fatty acid oxidation. In metabolic terms, toxicity of usnic acid can be predicted to be especially dangerous in the fasted state due to the combination of several deleterius events such as diminished hepatic glucose and ketone bodies output to the brain and increased ammonia production.

The action of p -synephrine on hepatic carbohydrate metabolism and respiration occurs via both Ca 2+ -mobilization and cAMP production

Citrus aurantium extracts, which contain large amounts of p-synephrine, are widely used for weight loss purposes and as appetite suppressants. In the liver, C. aurantium (bitter orange) extracts affect hemodynamics, carbohydrate metabolism, and oxygen uptake. The purpose of the present work was to quantify the action of p-synephrine and also to obtain indications about its mechanism of action, a task that would be difficult to accomplish with C. aurantium extracts due to their rather complex composition. The experimental system was the isolated perfused rat liver. p-Synephrine significantly stimulated glycogenolysis, glycolysis, gluconeogenesis, and oxygen uptake. The compound also increased the portal perfusion pressure and the redox state of the cytosolic NAD+/NADH couple. A Ca2+-dependency for both the hemodynamic and the metabolic effects of p-synephrine was found. p-Synephrine stimulated both cAMP overflow and the initial Ca2+ release from the cellular stores previously labeled with 45Ca2+. The metabolic and hemodynamic actions of p-synephrine were strongly inhibited by α-adrenergic antagonists and moderately affected by β-adrenergic antagonists. The results allow to conclude that p-synephrine presents important metabolic and hemodynamic effects in the liver. These effects can be considered as both catabolic (glycogenolysis) and anabolic (gluconeogenesis), they are mediated by both α- and β-adrenergic signaling, require the simultaneous participation of both Ca2+ and cAMP, and could be contributing to the overall stimulation of metabolism that usually occurs during weight loss periods.

Effects of an Agaricus blazei Aqueous Extract Pretreatment on Paracetamol-Induced Brain and Liver Injury in Rats

The action of an Agaricus blazei aqueous extract pretreatment on paracetamol injury in rats was examined not only in terms of the classical indicators (e.g., levels of hepatic enzymes in the plasma) but also in terms of functional and metabolic parameters (e.g., gluconeogenesis). Considering solely the classical indicators for tissue damage, the results can be regarded as an indication that the A. blazei extract is able to provide a reasonable degree of protection against the paracetamol injury in both the hepatic and brain tissues. The A. blazei pretreatment largely prevented the increased levels of hepatic enzymes in the plasma (ASP, ALT, LDH, and ALP) and practically normalized the TBARS levels in both liver and brain tissues. With respect to the functional and metabolic parameters of the liver, however, the extract provided little or no protection. This includes morphological signs of inflammation and the especially important functional parameter gluconeogenesis, which was impaired by paracetamol. Considering these results and the long list of extracts and substances that are said to have hepatoprotective effects, it would be useful to incorporate evaluations of functional parameters into the experimental protocols of studies aiming to attribute or refute effective hepatoprotective actions to natural products.

Purinergic Effects of a Hydroalcoholic Agaricus brasiliensis (A. blazei) Extract on Liver Functions

The effects of a hydroalcoholic extract of Agaricus brasiliensis (A. blazei) on functional parameters in the perfused rat liver were examined with emphasis on its content of nucleotides and nucleosides. Several nucleosides and nucleotides were identified in the A. brasiliensis extract, which was active on several liver functions. A significant part of the effects is the result of the purinergic action of nucleosides and nucleotides: pressure increment, glycogenolysis stimulation, transient inhibition of oxygen consumption, and redox state changes. Other phenomena such as the stimulation of gluconeogenesis, ureogenesis, and oxygen consumption are more likely consequences of the metabolic transformation of substrates contained within the extract, especially amino acids. It seems apparent that consumption of A. brasiliensis represents not only the ingestion of metabolic precursors but also the ingestion of substances that, even at low concentrations, can exert important signaling functions in the liver as well as in the organism as a whole.

Tadalafil inhibits the cAMP stimulated glucose output in the rat liver

The purpose of the present work was to verify if tadalafil affects hepatic glucose output, one of the primary targets of cAMP, in the isolated perfused rat liver. No effects on glycogen catabolism and oxygen uptake were found under basal conditions for tadalafil concentrations in the range between 0.25 and 10 μM. However, tadalafil had a clear and time-dependent inhibitory effect on the cAMP- and glucagon-stimulated glucose release. Constant infusion of tadalafil in the range between 0.25 and 10 μM eventually abolished 100% of the stimulatory action of those effectors. The tadalafil concentrations producing half-maximal rates of inhibition of the cAMP and glucagon stimulated glycogenolysis were 0.46±0.04 and 1.07±0.16 μM, respectively. These concentrations are close to the plasma peak concentrations in patients after ingestion of 20 mg tadalafil. The drug also diminished the activity of glycogen phosphorylase a and increased the activities of glucose 6-phosphatase, glucokinase, pyruvate kinase and glucose 6-phosphate dehydrogenase. These actions occurred only in the cellular environment. Tadalafil did not affect binding of cAMP to protein kinase A. Diminution of cAMP-stimulated glucose output is the opposite of what can be expected from a phosphodiesterase inhibition, the most common effect attributed to tadalafil. Diminution of glucose output by tadalafil can be attributed (a) to an interference with glycogen phosphorylase stimulation and (b) to an increased futile cycling of glucose 6-phosphate and glucose with a concomitant increased flow of hexose units into cellular metabolic pathways. The effects described in the present work may prove to represent important side effects of tadalafil.

Adrenergic Metabolic and Hemodynamic Effects of Octopamine in the Liver

The fruit extracts of Citrus aurantium (bitter orange) are traditionally used as weight-loss products and as appetite suppressants. A component of these extracts is octopamine, which is an adrenergic agent. Weight-loss and adrenergic actions are always related to metabolic changes and this work was designed to investigate a possible action of octopamine on liver metabolism. The isolated perfused rat liver was used to measure catabolic and anabolic pathways and hemodynamics. Octopamine increased glycogenolysis, glycolysis, oxygen uptake, gluconeogenesis and the portal perfusion pressure. Octopamine also accelerated the oxidation of exogenous fatty acids (octanoate and oleate), as revealed by the increase in 14CO2 production derived from 14C labeled precursors. The changes in glycogenolysis, oxygen uptake and perfusion pressure were almost completely abolished by α1-adrenergic antagonists. The same changes were partly sensitive to the β-adrenergic antagonist propranolol. It can be concluded that octopamine accelerates both catabolic and anabolic processes in the liver via adrenergic stimulation. Acceleration of oxygen uptake under substrate-free perfusion conditions also means acceleration of the oxidation of endogenous fatty acids, which are derived from lipolysis. All these effects are compatible with an overall stimulating effect of octopamine on metabolism, which is compatible with its reported weight-loss effects in experimental animals.