Changes in oxidative metabolism in selected tissues of the crab (Scylla serrata) in response to cadmium toxicity

Changes in oxidative metabolism were studied in hepatopancreas, muscle, and hemolymph of the edible crab Scylla serrata, exposed to a sublethal concentration (2.5 ppm) of cadmium chloride. A significant decrease in glycogen, total carbohydrates, and pyruvate and an increase in lactate levels in hepatopancreas and muscle were observed. Hemolymph sugar levels were increased in experimental crabs. An increase in phosphorylase suggested increased glycogenolysis during cadmium toxicity. The decrease in lactate dehydrogenase activity and the increase in lactate content indicated reduced mobilization of pyruvate into the citric acid cycle. Krebs cycle enzymes such as succinate dehydrogenase and malate dehydrogenase were found to be decreased, suggesting impairment of mitochondrial oxidative metabolism as a consequence of cadmium toxicity. Glucose-6-phosphate dehydrogenase activity was increased, suggesting enhanced oxidation of glucose by the HMP pathway. Cytochrome-c oxidase and Mg²⁺ ATPase activity levels decreased, indicating impaired energy synthesis during cadmium stress. Acid and alkaline phosphatase activities increased, suggesting enhanced breakdown of phosphates to release energy in view of impaired ATPase system during cadmium exposure. A significant decrease in protein and free amino acid and an increase in ammonia, urea, and glutamine levels were observed in the tissues during exposure. An increase in protease, alanine aminotransaminase, and asparate aminotransaminase suggested increased proteolysis and transamination of amino acids. The increase in glutamate dehydrogenase, AMP deaminase, and adenosine deaminase indicated increased ammonia production. The increased arginase and glutamine synthetase suggested the detoxification or mobilization of ammonia toward the production of urea and glutamine. These results suggest that cadmium affects oxidative metabolism and induces hyperammonemia, and crabs switch over their metabolic profiles toward compensatory mechanisms for the survivability in cadmium-polluted habitats.     

Effects of sublethal concentrations of phosphamidon, methyl parathion, DDT, and lindane on tissue nitrogen metabolism in the penaeid prawn, Metapenaeus monoceros (Fabricius).

Changes in midgut gland, muscle, and gill tissue nitrogen metabolic profiles studied in a penaeid prawn, Metapenaeus monoceros, following its exposure to sublethal concentrations of phosphamidon, methyl parathion, DDT, and lindane. In all the pesticide-exposed prawn tissues, ammonia levels were significantly increased and a shift in the nitrogen metabolism toward the synthesis of urea and glutamine was observed. Inhibition of glutamate oxidation to ammonia and alpha-ketoglutarate by glutamate dehydrogenase suggest a mechanism whereby hyperammonemia is reduced by minimizing the addition of further ammonia to the existing elevated ammonia. Aspartate (AAT) and alanine (AlAT) aminotransferases demonstrated an increase in their activity levels, suggesting gluconeogenesis. Pesticide-induced stress also seems to induce ammoniagenesis, which is due to increased deamination of purines. Mechanisms to detoxify the ammonia by enhancing the synthesis of urea and glutamine were observed in the tissues.     

Different metabolites might reduce food intake by the mitochondrial generation of reducing equivalents

To test the possibility that hypophagic effects of injected metabolites are linked to a particular oxidative step in their metabolism, cumulative food intake in rats after subcutaneous injection of various metabolites or their immediate oxidation products was investigated. Glycerol was compared with dihydroxyacetone, L-malate with oxaloacetate, and L-lactate with pyruvate. Subcutaneous injection of 4.5 mmol/kg metabolic body weight (BW0.75) of glycerol or malate reduced food intake significantly, whereas the same doses of dihydroxyacetone or oxaloacetate did not. Lactate or pyruvate (4.5 mmol/kg BW0.75, each) both reduced food intake significantly. However, even higher doses (7.7 mmol/kg BW0.75) of lactate or pyruvate failed to affect food intake when rats were fed a high fat (HF) diet, which is known to decrease the activity of the enzyme pyruvate dehydrogenase. In an additional experiment, subcutaneous injection of lactate or pyruvate (7.7 mmol/kg BW0.75, each) increased plasma levels of lactate and pyruvate 2 h after the injection in HF-rats more than in rats fed the usual high-carbohydrate diet. The data are consistent with the hypothesis that the increased generation of reducing equivalents in the mitochondria, brought about by the oxidation of injected glycerol, malate, lactate, or pyruvate, reduces food intake in rats.     

Glucose Metabolism in Cancer and Ischemia: Possible Therapeutic Consequences of the Warburg Effect

The Warburg effect states that the main source of energy for cancer cells is not aerobic respiration, but glycolysis—even in normoxia. The shift from one to the other is governed by mutually counteracting enzymes: pyruvate dehydrogenase and pyruvate dehydrogenase kinase (PDK). Anaerobic metabolism of cancer cells promotes cell proliferation, local tissue immunosuppression, resistance to hypoxic conditions, and metastatic processes. By switching glucose back to oxidative metabolism, these effects might be reversed. This can be achieved using PDK inhibitors, such as dichloroacetate. Patients suffering from ischemic conditions might benefit from this effect. On the other hand, the β-blockers (adrenergic β-antagonists) often used in these patients appear to improve cancer-specific survival, and nonselective β-blockers have been shown to promote glucose oxidation. Might there be a link?     

Metabolical effects of Folidol 600 on the neotropical freshwater fish matrinxã, Brycon cephalus

The neotropical freshwater fish matrinx?, Brycon cephalus (Günther, 1869), was exposed to 1/3 of 96 h-LC50 of Folidol 600 (methyl parathion) for 96 h and allowed to recover for 24, 48, 96, and 192 h. Acetylcholinesterase (AChE), alanine aminotransferase (ALAT), aspartate aminotransferase (AAT), lactate dehydrogenase (LDH), malate dehydrogenase (MDH), and glutamate dehydrogenase (GDH) were assayed in brain, liver, muscle, and plasma. Plasma and brain AChE activities were strongly inhibited (64% and 87%, respectively), remaining low in the brain during recovery. Liver ALAT decreased 59.4% and plasma ALAT increased 94.2%. This response, associated with GDH reduction during the recovery period, was attributed to impairment of amino acid metabolism and to liver damage. The increase of heart and plasma AAT suggested tissue injury. Liver and plasma LDH and MDH did not change during the exposure to Folidol, but liver MDH decreased 34% during recovery, indicating a failure of oxidative metabolism in such tissue. Hepatic glycogen and glucose levels decreased 80.4 and 55%, respectively, followed by glucose mobilization to the plasma. The hepatic and muscular profile of lactate after recovery suggested gluconeogenesis without tissue hypoxia. These results revealed that methyl parathion affects the intermediary metabolism of matrinx? and that the assayed enzymes can work as good biomarkers of organophosphorus pesticide contamination.     

Effect of 2,4-dinitrophenol on the energy metabolism of cattle embryos produced by in vitro fertilization and culture

In cattle embryos, the proportion of ATP produced by glycolysis increases following the major activation of the embryonic genome, and development to the blastocyst stage is improved in the presence of 10 microM 2,4-dinitrophenol (DNP), an uncoupler of oxidative phosphorylation, from Day 5 to Day 7 of culture. In Experiment 1 of the present study, culture of cattle embryos in the presence of 10 microM DNP from Day 5 to Day 7 stimulated development to the blastocyst stage, but had no significant effects on oxygen, pyruvate or glucose uptake, or on lactate production. In Experiment 2, culture of cattle embryos in the presence of 10 microM DNP from Day 5 to Day 7, stimulated the metabolism of [2-14C]pyruvate (a measure of Krebs cycle activity) on all of Days 5, 6 and 7, and stimulated metabolism of [5-3H]glucose (a measure of glycolysis) on Day 7 only. The results show that 10 microM DNP stimulates oxidative and glycolytic metabolism in Day-5 to Day-7 cattle embryos, but this does not fully explain the observed increase in developmental competence. We propose that partial inhibition or uncoupling of oxidative phosphorylation may reduce the level of intracellular reactive oxygen species production, thereby facilitating development.     

Regulation of skeletal muscle amino acid metabolism during exercise

The contribution of amino acid oxidation to total energy expenditure is negligible during short-term intense exercise and accounts for 3-6% of the total adenosine triphosphate supplied during prolonged exercise in humans. While not quantitatively important in terms of energy supply, the intermediary metabolism of several amino acids-notably glutamate, alanine, and the branched-chain amino acids-affects other metabolites, including the intermediates within the tricarboxylic acid (TCA) cycle. Glutamate appears to be a key substrate for the rapid increase in muscle TCA cycle intermediates (TCAI) that occurs at the onset of moderate to intense exercise, due to a rightward shift of the reaction catalyzed by alanine aminotransferase (glutamate + pyruvate <==> alanine + 2-oxoglutarate). The pool of muscle TCAI declines during prolonged exercise, and this has been attributed to an increase in leucine oxidation that relies on one of the TCAI. However, this mechanism does not appear to be quantitatively important due of the relatively low maximal activity of branched-chain oxoacid dehydrogenase, the key enzyme involved. It has been suggested that an increase in TCAI is necessary to attain high rates of aerobic energy production and that a decline in TCAI may be a causative factor in local muscle fatigue. These topics remain controversial, but recent evidence suggests that changes in TCAI during exercise are unrelated to oxidative energy provision in skeletal muscle.     

Effect of Ethyl Pyruvate on Skeletal Muscle Metabolism in Rats Fed on a High Fat Diet

Impaired mitochondrial capacity may be implicated in the pathology of chronic metabolic diseases. To elucidate the effect of ethyl pyruvate supplementation on skeletal muscles metabolism we examined changes in activities of mitochondrial and antioxidant enzymes, as well as sulfhydryl groups oxidation (an indirect marker of oxidative stress) during the development of obesity. After 6 weeks feeding of control or high fat diet, Wistar rats were divided into four groups: control diet, control diet and ethyl pyruvate, high fat diet, and high fat diet and ethyl pyruvate. Ethyl pyruvate was administered as 0.3% solution in drinking water, for the following 6 weeks. High fat diet feeding induced the increase of activities 3-hydroxyacylCoA dehydrogenase, citrate synthase, and fumarase. Moreover, higher catalase and superoxide dismutase activities, as well as sulfhydryl groups oxidation, were noted. Ethyl pyruvate supplementation did not affect the mitochondrial enzymes’ activities, but induced superoxide dismutase activity and sulfhydryl groups oxidation. All of the changes were observed in soleus muscle, but not in extensor digitorum longus muscle. Additionally, positive correlations between fasting blood insulin concentration and activities of catalase (p = 0.04), and superoxide dismutase (p = 0.01) in soleus muscle were noticed. Prolonged ethyl pyruvate consumption elevated insulin concentration, which may cause modifications in oxidative type skeletal muscles.     

Decline of Lactate in Tumor Tissue After Ketogenic Diet: In Vivo Microdialysis Study in Patients with Head and Neck Cancer

In head and neck squamous cell carcinoma (HNSCC) aerobic glycolysis is the key feature for energy supply of the tumor. Quantitative microdialysis (μD) offers an online method to measure parameters of the carbohydrate metabolism in vivo. The aim was to standardize a quantitative μD-study in patients with HNSCC and to prove if a ketogenic diet would differently influence the carbohydrate metabolism of the tumor tissue. Commercially available 100 kDa-CMA71-μD- catheters were implanted in tumor-free and in tumor tissue in patients with HNSCC for simultaneous measurements up to 5 days. The metabolic pattern and circadian rhythm of urea, glucose, lactate, and pyruvate was monitored during 24 h of western diet and subsequent up to 4 days of ketogenic diet. After 3 days of ketogenic diet the mean lactate concentration declines to a greater extent in the tumor tissue than in the tumor-free mucosa, whereas the mean glucose and pyruvate concentrations rise. The in vivo glucose metabolism of the tumor tissue is clearly influenced by nutrition. The decline of mean lactate concentration in the tumor tissue after ketogenic diet supports the hypothesis that HNSCC tumor cells might use lactate as fuel for oxidative glucose metabolism.     

The use of biomarkers in Daphnia magna toxicity testing V. In vivo alterations in the carbohydrate metabolism of Daphnia magna exposed to sublethal concentrations of mercury and lindane

Aspects of the carbohydrate metabolism of Daphnia magna exposed for 48 and 96 h to sublethal concentrations of mercury and lindane were investigated. General as well as toxicant-specific perturbations in the intermediary metabolism were observed. Both model toxicants caused an increase in glycolytic and hexose-monophosphate shunt activity. Mercury exposure increased lactate dehydrogenase and isocitrate activity (only after 96 h), while lindane exposure, on the contrary, inhibited the cellular lactate formation and increased the Krebs' cycle activity (only after 48 h). Daphnids exposed to sublethal mercury concentrations clearly exhibited increased glycogenolytic activity, while in lindane-exposed organisms mainly glycogen phosphorylase inhibition was detected. The short-term enzyme-based effect levels (48--96 h LOEC and EC(10) values) were compared with the effects on the population dynamics. This evaluation for both model toxicants suggests that threshold levels (LOEC or EC(10) values) based on pyruvate kinase activity after 48 and 96 h of exposure could be potential early warning signals for long-term effects. A set of enzymatic endpoints, based on the intermediary metabolism, is suggested to characterize the metabolic state of the daphnids.     

The effect of NO2 on erythrocyte glucose metabolism as related to changes in redox ratio [NAD+]/[NADH].

Glucose utilization of human erythrocytes increased to approximately 2.5 times control values when exposed to a mean NO₂ concentration of 336.6 ppm for 2 hours at 37°C and pH = 7.23. The fraction of glucose utilized by the pentose phosphate pathway remained constant so that actual glucose utilized by both this pathway and by glycolysis increased in proportion to the total glucose metabolized. The rate of total lactate plus pyruvate production remained unchanged. These data suggest that NO₂ may influence several loci of erythrocyte metabolism, including accumulation of glycolytic intermediates proximal to the reaction catalyzed by glyceraldehyde-3-phosphate dehydrogenase, oxidation of NADH, NADPH, and GSH, and alteration of NADH dependent enzymes.     

Toxicity of the pyrethroid insecticide fenvalerate to a fresh water fish, Tilapia mossambica (Peters): changes in glycogen metabolism of muscle

Toxic effects of a pyrethroid insecticide, fenvalerate, on fish muscle glycogen metabolism were investigated. Estimations were made after 10 and 20 days of exposure, and altered muscle glycogen metabolism was observed. The changes included a significant (P less than 0.001) decrease in the levels of glycogen, pyruvate, maleate dehydrogenase (MDH), succinate dehydrogenase (SDH), and phosphorylase a, b, and ab activities, while elevated levels of lactic acid, aldolase, and lactate dehydrogenase (LDH) activity were observed under fenvalerate intoxication. There was a decrease in opercular movement and oxygen consumption with an increase in concentration of fenvalerate.     

Effect of nitrite on ureagenesis and carbohydrate metabolism in isolated rat hepatocytes

The effect of three NaNO₂ concentrations (0.5, 2.0, and 5.0 mM) on¹⁵N-ammonia utilization, ureagenesis, glucose, pyruvate and lactate formation and glycogen breakdown were studied in isolated rat hepatocytes. Nitrite failed to affect the rate of glycogenolysis as well as the lactate and pyruvate formation, but at the same time it markedly increased the glucose formation. It is concluded that the increase in the glucose formation results from the nitrite stimulation of the rate of gluconeogenesis.An increased sodium nitrite concentration caused a significant decrease in the ammonia utilization and urea synthesis; there are strong linear correlations between the nitrite concentration and the amount of utilized ammonia (r = –0.93) and the formed urea (r = –0.96). The observed lower rate of ureagenesis in the presence of nitrite resulted from the diminished incorporation of the added¹⁵N-ammonia into urea, as well as from the diminished urea formation from endogenous nitrogen.It is concluded that the disturbances in carbohydrate and nitrogen metabolism observed in the nitrite-poisoned animals are attributed to the direct effect of nitrite on metabolism.     

Glucose utilization by sheep embryos derived in vivo and in vitro.

Embryos were collected from superovulated donors at various intervals from onset of oestrus, ranging from Day 1.5 to Day 6. In addition, blastocysts obtained from the culture of 1-cell embryos collected in vivo or of oocytes matured and fertilized in vitro were used to assess the effects of in vitro manipulation and culture on glucose utilization. Glycolytic activity was determined by the conversion of [5-3H]glucose to 3H2O, and oxidation of glucose was determined by the conversion of [U-14C]glucose to 14CO2. Glucose utilization increases significantly from the 8-cell stage and during compaction and blastulation. Glucose oxidation was at a relatively low level (5-12% of total utilization) compared with glycolysis. No difference was observed between the glycolytic activity of blastocysts derived from in vivo or in vitro sources. However, glucose oxidation was lower (P less than 0.05) in blastocysts derived from the culture of 1-cell embryos or from oocytes matured and fertilized in vitro. Exogenous tricarboxylic acid cycle substrates (i.e. pyruvate and lactate supplied in the medium) affected the level of glucose oxidation.     

Oxidative metabolic activity of boar spermatozoa: a system for assessing anti-glycolytic activity of potential inhibitors in vitro

The oxidative metabolic capability of mature boar spermatozoa has been determined in vitro. The high rate of oxidation of fructose, glucose, glycerol, glycerol-3-phosphate and lactate to CO2 and the optimization of incubation conditions indicates that these cells could constitute a model system for investigating the anti-glycolytic activity of potential male anti-fertility agents. The effects of several chemical agents on the oxidative metabolism of boar spermatozoa are reported.     

The effect of chronic ethanol ingestion on myocardial glucose and energy metabolism

To determine the effect of chronic alcohol ingestion, rats were given 15 or 25% v/v of alcohol in water for a period of 6 months. The activities of some key enzymes involved in the metabolism of glucose, mitochondrial respiratory rates, and efficiency of oxidative phosphorylation were studied in the hearts of alcohol-treated and untreated rats. In the group receiving 15% alcohol, glucose-6-phosphate dehydrogenase (G-6-PDH) was elevated. In rats given 25% alcohol, activities of G-6-PDH, aldolase, and glyceraldehyde phosphate dehydrogenase were elevated but isocitrate dehydrogenase was reduced. Mitochondrial respiratory rates and the efficiency of phosphorylation were depressed in rats given 25% of alcohol. Except for mitochondrial oxidation of pyruvate and alpha-ketoglutarate, all biochemical parameters studied were within normal limits a month after alcohol was discontinued.     

Suppression of glycogen consumption during acute exercise by dietary branched-chain amino acids in rats

The effects of a diet supplemented with branched-chain amino acids (BCAA; 4.8% or 6.2%) on BCAA catabolism and glycogen metabolism in rats were examined. Rats were fed a BCAA diet or control diet for 4 wk and part of the rats were subjected to exercise training during the experimental period. Feeding the BCAA diet increased serum BCAA concentrations and activity of the hepatic branched-chain alpha-keto acid dehydrogenase complex, the rate-limiting enzyme in the catabolism of BCAA, suggesting that dietary BCAA promotes BCAA catabolism. Although the serum glucose concentration and glycogen contents in the liver and gastrocnemius muscle of rested rats were not significantly affected by feeding of the BCAA diet, those in rats exhausted by acute exercise were 2-4-fold higher in rats fed the BCAA diet than in rats fed the control diet. The activity of pyruvate dehydrogenase complex in the liver and gastrocnemius muscle after acute exercise showed reverse trends; the complex activities (especially in liver) tended to be less in the BCAA diet group than in the control diet group. These results suggest that dietary BCAA spares glycogen stores in liver and skeletal muscle during exercise and that the decrease in pyruvate dehydrogenase complex activity in these tissues by dietary BCAA is involved in the mechanisms.     

Triacylglycerol infusion improves exercise endurance in patients with mitochondrial myopathy due to complex I deficiency

BACKGROUND: A high-fat diet has been recommended for the treatment of patients with mitochondrial myopathy due to complex I (NADH dehydrogenase) deficiency (CID). OBJECTIVE: This study evaluated the effects of intravenous infusion of isoenergetic amounts of triacylglycerol or glucose on substrate oxidation, glycolytic carbohydrate metabolism, and exercise endurance time and energy state of muscle in CID patients. DESIGN: Four CID patients and 15 control subjects were infused with triacylglycerol (3.7 mg x kg(-1) x min(-1)) or glucose (10 mg x kg(-1) x min(-1)) during low-intensity leg exercise. Respiratory calorimetry was used to evaluate mitochondrial substrate oxidation. The concentration and rate of appearance of plasma lactate (from dilution of [1-(13)C]lactate) were used to evaluate glycolytic carbohydrate metabolism. (31)P magnetic resonance spectroscopy was used to determine ratios of phosphocreatine to inorganic o-phosphate in forearm muscle during exercise. RESULTS: In 3 patients, leg exercise endurance time was better during the triacylglycerol infusion than during the glucose infusion. In all 4 patients, whole-body oxygen consumption rates during exercise were higher during triacylglycerol infusion than during the glucose infusion. In 3 patients, the concentration and rate of appearance of plasma lactate were lower during triacylglycerol infusion than during the glucose infusion. Ratios of phosphocreatine to inorganic o-phosphate during exercise were not significantly different between the 2 infusion studies or between the patients and control subjects. CONCLUSIONS: Triacylglycerol infusion is associated with a greater oxidation of substrates, lower rates of appearance and concentrations of plasma lactate, and greater leg exercise endurance time in myopathic CID patients than is glucose infusion. The energy state of muscle during exercise, however, was not significantly different after infusion of triacylglycerol or glucose.