Effects of fou8/fry1 mutation on sulfur metabolism: is decreased internal sulfate the trigger of sulfate starvation response?

The fou8 loss of function allele of adenosine bisphosphate phosphatase FIERY1 results in numerous phenotypes including the increased enzymatic oxygenation of fatty acids and increased jasmonate synthesis. Here we show that the mutation causes also profound alterations of sulfur metabolism. The fou8 mutants possess lower levels of sulfated secondary compounds, glucosinolates, and accumulate the desulfo-precursors similar to previously described mutants in adenosine 5'phosphosulfate kinase. Transcript levels of genes involved in sulfate assimilation differ in fou8 compared to wild type Col-0 plants and are similar to plants subjected to sulfate deficiency. Indeed, independent microarray analyses of various alleles of mutants in FIERY1 showed similar patterns of gene expression as in sulfate deficient plants. This was not caused by alterations in signalling, as the fou8 mutants contained significantly lower levels of sulfate and glutathione and, consequently, of total elemental sulfur. Analysis of mutants with altered levels of sulfate and glutathione confirmed the correlation of sulfate deficiency-like gene expression pattern with low internal sulfate but not low glutathione. The changes in sulfur metabolism in fou8 correlated with massive increases in 3'-phosphoadenosine 5'-phosphate levels. The analysis of fou8 thus revealed that sulfate starvation response is triggered by a decrease in internal sulfate as opposed to external sulfate availability and that the presence of desulfo-glucosinolates does not induce the glucosinolate synthesis network. However, as well as resolving these important questions on the regulation of sulfate assimilation in plants, fou8 has also opened an array of new questions on the links between jasmonate synthesis and sulfur metabolism.

New approach for weight reduction by a combination of diet, light resistance exercise and the timing of ingesting a protein supplement.

We have reported that ingesting a meal immediately after exercise increased skeletal muscle accretion and less adipose tissue accumulation in rats employed in a 10 week resistance exercise program. We hypothesized that a possible increase in the resting metabolic rate (RMR) as a result of the larger skeletal muscle mass might be responsible for the less adipose deposition. Therefore, the effect of the timing of a protein supplement after resistance exercise on body composition and the RMR was investigated in 17 slightly overweight men. The subjects participated in a 12-week weight reduction program consisting of mild energy restriction (17% energy intake reduction) and a light resistance exercise using a pair of dumbbells (3-5 kg). The subjects were assigned to two groups. Group S ingested a protein supplement (10 g protein, 7 g carbohydrate, 3.3 g fat and one-third of recommended daily allowance (RDA) of vitamins and minerals) immediately after exercise. Group C did not ingest the supplement. Daily intake of both energy and protein was equal between the two groups and the protein intake met the RDA. After 12 weeks, the bodyweight, skinfold thickness, girth of waist and hip and percentage bodyfat significantly decreased in the both groups, however, no significant differences were observed between the groups. The fat-free mass significantly decreased in C, whereas its decrease in S was not significant. The RMR and post-meal total energy output significantly increased in S, while these variables did not change in C. In addition, the urinary nitrogen excretion tended to increase in C but not in S. These results suggest that the RMR increase observed in S might be associated with an increase in body protein synthesis.

Effect of bicarbonate and lactate buffer on glucose and lactate metabolism during hemodiafiltration in patients with multiple organ failure.

OBJECTIVE: To compare the effects of sodium bicarbonate and lactate for continuous veno-venous hemodiafiltration (CVVHDF) in critically ill patients. DESIGN AND SETTINGS: Prospective crossed-over controlled trial in the surgical and medical ICUs of a university hospital. PATIENTS: Eight patients with multiple organ dysfunction syndrome (MODS) requiring CVVHDF. INTERVENTION: Each patient received the two buffers in a randomized sequence over two consecutive days. MEASUREMENTS AND RESULTS: The following variables were determined: acid-base parameters, lactate production and utilization ((13)C lactate infusion), glucose turnover (6,6(2)H(2)-glucose), gas exchange (indirect calorimetry). No side effect was observed during lactate administration. Baseline arterial acid-base variables were equal with the two buffers. Arterial lactate (2.9 versus 1.5 mmol/l), glycemia (+18%) and glucose turnover (+23%) were higher in the lactate period. Bicarbonate and glucose losses in CVVHDF were substantial, but not lactate elimination. Infusing (13)C lactate increased plasma lactate levels equally with the two buffers. Lactate clearance (7.8+/-0.8 vs 7.5+/-0.8 ml/kg per min in the bicarbonate and lactate periods) and endogenous production rates (14.0+/-2.6 vs 13.6+/-2.6 mmol/kg per min) were similar. (13)C lactate was used as a metabolic substrate, as shown by (13)CO(2) excretion. Glycemia and metabolic rate increased significantly and similarly during the two periods during lactate infusion. CONCLUSION: Lactate was rapidly cleared from the blood of critically ill patients without acute liver failure requiring CVVHDF, being transformed into glucose or oxidized. Lactate did not exert undesirable effects, except moderate hyperglycemia, and achieved comparable effects on acid-base balance to bicarbonate.

Kinetics of dexamethasone-induced alterations of glucose metabolism in healthy humans.

Six healthy human subjects were studied during three 75-g oral, [13C]glucose tolerance tests to assess the kinetics of dexamethasone-induced impairment of glucose tolerance. On one occasion, they received dexamethasone (4 x 0.5 mg/day) during the previous 2 days. On another occasion, they received a single dose (0. 5 mg) of dexamethasone 150 min before ingestion of the glucose load. On the third occasion, they received a placebo. Postload plasma glucose was significantly increased after both 2 days dexamethasone and single dose dexamethasone compared with control (P < 0.05). This corresponded to a 20-23% decrease in the metabolic clearance rate of glucose, whereas total glucose turnover ([6,6-2H]glucose), total (indirect calorimetry) and exogenous glucose oxidation (13CO2 production), and suppression of endogenous glucose production were unaffected by dexamethasone. Plasma insulin concentrations were increased after 2 days of dexamethasone but not after a single dose of dexamethasone. In a second set of experiments, the effect of a single dose of dexamethasone on insulin sensitivity was assessed in six healthy humans during a 2-h euglycemic hyperinsulinemic clamp. Dexamethasone did not significantly alter insulin sensitivity. It is concluded that acute administration of dexamethasone impairs oral glucose tolerance without significantly decreasing insulin sensitivity.

PPARalpha governs glycerol metabolism.

Glycerol, a product of adipose tissue lipolysis, is an important substrate for hepatic glucose synthesis. However, little is known about the regulation of hepatic glycerol metabolism. Here we show that several genes involved in the hepatic metabolism of glycerol, i.e., cytosolic and mitochondrial glycerol 3-phosphate dehydrogenase (GPDH), glycerol kinase, and glycerol transporters aquaporin 3 and 9, are upregulated by fasting in wild-type mice but not in mice lacking PPARalpha. Furthermore, expression of these genes was induced by the PPARalpha agonist Wy14643 in wild-type but not PPARalpha-null mice. In adipocytes, which express high levels of PPARgamma, expression of cytosolic GPDH was enhanced by PPARgamma and beta/delta agonists, while expression was decreased in PPARgamma(+/-) and PPARbeta/delta(-/-) mice. Transactivation, gel shift, and chromatin immunoprecipitation experiments demonstrated that cytosolic GPDH is a direct PPAR target gene. In line with a stimulating role of PPARalpha in hepatic glycerol utilization, administration of synthetic PPARalpha agonists in mice and humans decreased plasma glycerol. Finally, hepatic glucose production was decreased in PPARalpha-null mice simultaneously fasted and exposed to Wy14643, suggesting that the stimulatory effect of PPARalpha on gluconeogenic gene expression was translated at the functional level. Overall, these data indicate that PPARalpha directly governs glycerol metabolism in liver, whereas PPARgamma regulates glycerol metabolism in adipose tissue.

Cerebral and extracerebral cholesterol metabolism and CSF markers of Alzheimer's disease.

The disturbances of the cholesterol synthesis and metabolism described in Alzheimer's disease (AD) may be both a consequence of the neurodegenerative process and a contributor to the pathogenesis. These putative relationships and their underlying mechanisms are not well understood. The aim of this study was to evaluate the relationship between the cerebral and extracerebral cholesterol synthesis and metabolism, and the AD pathology as reflected by CSF markers in humans. We evaluated the relationships between the plasma and the cerebrospinal fluid (CSF) concentrations of cholesterol, the cholesterol precursors lanosterol, lathosterol and desmosterol, and the cholesterol elimination products 24S-hydroxycholesterol and 27-hydroxycholesterol, and the CSF markers for AD pathology Aβ1-42 and p-tau181 in 86 subjects with normal cognition and in 107 AD patients. CSF desmosterol, cholesterol and 24S-hydroxycholesterol in the AD group, and CSF 24S-hydroxycholesterol in the control group correlated with the p-tau181 levels. Neither CSF nor plasma concentrations of the included compounds correlated with the CSF Aβ1-42 levels. In multivariate regression tests including age, gender, albumin ratio, number of the APOEε4 alleles, and diagnosis, p-tau181 levels independently predicted the CSF desmosterol, cholesterol and 24S-hydroxycholesterol concentrations. The associations remained significant for CSF cholesterol and 24S-hydroxycholesterol when analyses were separately performed in the AD group. The results suggest that alterations of CNS cholesterol de novo genesis and metabolism are related to neurodegeneration and in particular to the cerebral accumulation of phosphorylated tau.

Drug metabolism for the perplexed medicinal chemist.

Two related and significant issues may elicit perplexity in medicinal chemists and are discussed here. First, a broad presentation of the pharmacological and toxicological consequences of drug metabolism should justify the significance of drug metabolism and serve as an incentive to further study. When comparing the pharmacological activities of a drug and its metabolite(s), a continuum is found which ranges from soft drugs (no active metabolites) to prodrugs (inactive per se, as illustrated here with clopidogrel and prasugrel). Innumerable intermediate cases document drugs whose activity is shared by one or more metabolites, as exemplified with tamoxifen. The toxicological consequences of metabolism at the molecular, macromolecular, and macroscopic levels are manyfold. A brief overview is offered together with a summary of the reactions of toxification and detoxification of the antiepileptic valproic acid. The second issue discussed in the review is a comparison of the relative significance of cytochromes P450 and other oxidoreductases (EC 1), hydrolases (EC 3), and transferases (EC 2) in drug metabolism, based on a 'guesstimate' of the number of drug metabolites that are known to be produced by them. The conclusion is that oxidoreductases are the main enzymes responsible for the formation of toxic or active metabolites, whereas transferases play the major role in producing inactive and nontoxic metabolites.

Evidence for catabolic pathway of propionate metabolism in CNS: expression pattern of methylmalonyl-CoA mutase and propionyl-CoA carboxylase alpha-subunit in developing and adult rat brain.

Methylmalonyl-CoA mutase (MCM) and propionyl-CoA carboxylase (PCC) are the key enzymes of the catabolic pathway of propionate metabolism and are mainly expressed in liver, kidney and heart. Deficiency of these enzymes leads to two classical organic acidurias: methylmalonic and propionic aciduria. Patients with these diseases suffer from a whole spectrum of neurological manifestations that are limiting their quality of life. Current treatment does not seem to effectively prevent neurological deterioration and pathophysiological mechanisms are poorly understood. In this article we show evidence for the expression of the catabolic pathway of propionate metabolism in the developing and adult rat CNS. Both, MCM and PCC enzymes are co-expressed in neurons and found in all regions of the CNS. Disease-specific metabolites such as methylmalonate, propionyl-CoA and 2-methylcitrate could thus be formed autonomously in the CNS and contribute to the pathophysiological mechanisms of neurotoxicity. In rat embryos (E15.5 and E18.5), MCM and PCC show a much higher expression level in the entire CNS than in the liver, suggesting a different, but important function of this pathway during brain development.

Glycogen metabolism as a marker of astrocyte differentiation.

Glycogen is a hallmark of mature astrocytes, but its emergence during astrocytic differentiation is unclear. Differentiation of E14 mouse neurospheres into astrocytes was induced with fetal bovine serum (FBS), Leukemia Inhibitory Factor (LIF), or Ciliary Neurotrophic Factor (CNTF). Cytochemical and enzymatic analyses showed that glycogen is present in FBS- or LIF- but not in CNTF-differentiated astrocytes. Glycogenolysis was induced in FBS- and LIF-differentiated astrocytes but glycogen resynthesis was observed only with FBS. Protein targeting to glycogen mRNA expression appeared with glial fibrillary acidic protein and S100beta in FBS and LIF conditions but not with CNTF. These results show that glycogen metabolism constitutes a useful marker of astrocyte differentiation.

Effects of endotoxin on lactate metabolism in humans.

ABSTRACT: INTRODUCTION: Hyperlactatemia represents one prominent component of the metabolic response to sepsis. In critically ill patients, hyperlactatemia is related to the severity of the underlying condition. Both an increased production and a decreased utilization and clearance might be involved in this process, but their relative contribution remains unknown. The present study aimed at assessing systemic and muscle lactate production and systemic lactate clearance in healthy human volunteers, using intravenous endotoxin (LPS) challenge. METHODS: Fourteen healthy male volunteers were enrolled in 2 consecutive studies (n = 6 in trial 1 and n = 8 in trial 2). Each subject took part in one of two investigation days (LPS-day with endotoxin injection and placebo-day with saline injection) separated by one week at least and in a random order. In trial 1, their muscle lactate metabolism was monitored using microdialysis. In trial 2, their systemic lactate metabolism was monitored by means of a constant infusion of exogenous lactate. Energy metabolism was monitored by indirect calorimetry and glucose kinetics was measured with 6,6-H2 glucose. RESULTS: In both trials, LPS increased energy expenditure (p = 0.011), lipid oxidation (p<0.0001), and plasma lactate concentration (p = 0.016). In trial 1, lactate concentration in the muscle microdialysate was higher than in blood, indicating lactate production by muscles. This was, however, similar with and without LPS. In trial 2, calculated systemic lactate production increased after LPS (p = 0.031), while lactate clearance remained unchanged. CONCLUSIONS: LPS administration increases lactatemia by increasing lactate production rather than by decreasing lactate clearance. Muscle is, however, unlikely to be a major contributor to this increase in lactate production. TRIAL REGISTRATION: ClinicalTrials.gov NCT01647997.

Training in hypoxia fails to further enhance endurance performance and lactate clearance in well-trained men and impairs glucose metabolism during prolonged exercise.

The aim of this study was to investigate the synergistic effects of endurance training and hypoxia on endurance performance in normoxic and hypoxic conditions (approximately 3000 m above sea level) as well as on lactate and glucose metabolism during prolonged exercise. For this purpose, 14 well-trained cyclists performed 12 training sessions in conditions of normobaric hypoxia (HYP group, n = 7) or normoxia (NOR group, n = 7) over 4 weeks. Before and after training, lactate and glucose turnover rates were measured by infusion of exogenous lactate and stable isotope tracers. Endurance performance was assessed during incremental tests performed in normoxia and hypoxia and a 40 km time trial performed in normoxia. After training, performance was similarly and significantly improved in the NOR and HYP groups (training, P < 0.001) in normoxic conditions. No further effect of hypoxic training was found on markers of endurance performance in hypoxia (training x hypoxia interaction, n.s.). In addition, training and hypoxia had no significant effect on lactate turnover rate. In contrast, there was a significant interaction of training and hypoxia (P < 0.05) on glucose metabolism, as follows: plasma insulin and glucose concentrations were significantly increased; glucose metabolic clearance rate was decreased; and the insulin to glucagon ratio was increased after training in the HYP group. In conclusion, our results show that, compared with training in normoxia, training in hypoxia has no further effect on endurance performance in both normoxic and hypoxic conditions or on lactate metabolic clearance rate. Additionally, these findings suggest that training in hypoxia impairs blood glucose regulation in endurance-trained subjects during exercise.

Inhibition of Na(+)-K(+)-ATPase by digoxin and its relation with energy expenditure and nutrient oxidation rate.

This study investigates the effects of digoxin, an inhibitor of the Na+ pump (Na(+)-K(+)-ATPase), on resting metabolic rate (RMR), respiratory quotient (RQ), and nutrient oxidation rate. Twelve healthy male subjects followed a double-blind protocol design and received either 1 mg/day digoxin or a placebo 2 days before indirect calorimetry measurements. Digoxin induced a 0.22 +/- 0.07 kJ/min or 3.8 +/- 1.5% (mean +/- SE, P = 0.01) decrease in RMR and a 0.40 +/- 0.13 kJ/min (P = 0.01) decrease in fat oxidation rate, whereas carbohydrate and protein oxidation rates did not change significantly. A dose-response relationship between serum digoxin and RQ was observed. These results suggest that digoxin reduces not only RMR but also fat oxidation rate by mechanisms that remain to be elucidated. Because a linkage and an association between genes coding the Na(+)-K(+)-ATPase and the RQ have been previously observed, the present demonstration of an effect of Na(+)-K(+)-ATPase inhibition on fat oxidation rate strengthens the concept that the activity of this enzyme may play a role in body weight regulation.

Circadian clock-coordinated 12 Hr period rhythmic activation of the IRE1alpha pathway controls lipid metabolism in mouse liver.

The mammalian circadian clock plays a fundamental role in the liver by regulating fatty acid, glucose, and xenobiotic metabolism. Impairment of this rhythm has been shown to lead to diverse pathologies, including metabolic syndrome. Currently, it is supposed that the circadian clock regulates metabolism mostly by regulating expression of liver enzymes at the transcriptional level. Here, we show that the circadian clock also controls hepatic metabolism by synchronizing a secondary 12 hr period rhythm characterized by rhythmic activation of the IRE1alpha pathway in the endoplasmic reticulum. The absence of circadian clock perturbs this secondary clock and provokes deregulation of endoplasmic reticulum-localized enzymes. This leads to impaired lipid metabolism, resulting in aberrant activation of the sterol-regulated SREBP transcription factors. The resulting aberrant circadian lipid metabolism in mice devoid of the circadian clock could be involved in the appearance of the associated metabolic syndrome.

Effect of olive oil on early and late events of colon carcinogenesis in rats: modulation of arachidonic acid metabolism and local prostaglandin E2 synthesis.

BACKGROUND Animal model studies have shown that the colon tumour promoting effect of dietary fat depends not only on the amount but on its fatty acid composition. With respect to this, the effect of n9 fatty acids, present in olive oil, on colon carcinogenesis has been scarcely investigated. AIMS To assess the effect of an n9 fat diet on precancer events, carcinoma development, and changes in mucosal fatty acid composition and prostaglandin (PG)E2 formation in male Sprague-Dawley rats with azoxymethane induced colon cancer. METHODS Rats were divided into three groups to receive isocaloric diets (5% of the energy as fat) rich in n9, n3, or n6 fat, and were administered azoxymethane subcutaneously once a week for 11 weeks at a dose rate of 7.4 mg/kg body weight. Vehicle treated groups received an equal volume of normal saline. Groups of animals were colectomised at weeks 12 and 19 after the first dose of azoxymethane or saline. Mucosal fatty acids were assessed at 12 and 19 weeks. Aberrant crypt foci and the in vivo intracolonic release of PGE2 were assessed at week 12, and tumour formation at week 19. RESULTS Rats on the n6 diet were found to have colonic aberrant crypt foci and adenocarcinomas more often than those consuming either the n9 or n3 diet. There were no differences between the rats on the n9 and n3 diets. On the other hand, administration of both n9 and n3 diets was associated with a decrease in mucosal arachidonate concentrations as compared with the n6 diet. Carcinogen treatment induced an appreciable increase in PGE2 formation in rats fed the n6 diet, but not in those fed the n3 and n9 diets. CONCLUSIONS Dietary olive oil prevented the development of aberrant crypt foci and colon carcinomas in rats, suggesting that olive oil may have chemopreventive activity against colon carcinogenesis. These effects may be partly due to modulation of arachidonic acid metabolism and local PGE2synthesis.

Genetic evidence for a role of adiponutrin in the metabolism of apolipoprotein B-containing lipoproteins.

Adiponutrin (PNPLA3) is a predominantly liver-expressed transmembrane protein with phospholipase activity that is regulated by fasting and feeding. Recent genome-wide association studies identified PNPLA3 to be associated with hepatic fat content and liver function, thus pointing to a possible involvement in the hepatic lipoprotein metabolism. The aim of this study was to examine the association between two common variants in the adiponutrin gene and parameters of lipoprotein metabolism in 23,274 participants from eight independent West-Eurasian study populations including six population-based studies [Bruneck (n = 800), KORA S3/F3 (n = 1644), KORA S4/F4 (n = 1814), CoLaus (n = 5435), SHIP (n = 4012), Rotterdam (n = 5967)], the SAPHIR Study as a healthy working population (n = 1738) and the Utah Obesity Case-Control Study including a group of 1037 severely obese individuals (average BMI 46 kg/m2) and 827 controls from the same geographical region of Utah. We observed a strong additive association of a common non-synonymous variant within adiponutrin (rs738409) with age-, gender-, and alanine-aminotransferase-adjusted lipoprotein concentrations: each copy of the minor allele decreased levels of total cholesterol on average by 2.43 mg/dl (P = 8.87 x 10(-7)), non-HDL cholesterol levels by 2.35 mg/dl (P = 2.27 x 10(-6)) and LDL cholesterol levels by 1.48 mg/dl (P = 7.99 x 10(-4)). These associations remained significant after correction for multiple testing. We did not observe clear evidence for associations with HDL cholesterol or triglyceride concentrations. In conclusion, our study suggests that adiponutrin is involved in the metabolism of apoB-containing lipoproteins.