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PubMed1988

Ethionine-induced alterations of enzymes involved in lipid metabolism and their possible relationship to induction of fatty liver.

Changes of enzymes involved in the hepatic metabolism of long-chain fatty acids (palmitoyl-CoA synthetase (EC 6.2.1.3), carnitine palmitoyltransferase (EC 6.2.1.3), glycerophosphate acyltransferase (EC 2.3.1.15)) in the liver of male rats were examined after ethionine exposure. Ethionine administration resulted in a dose- and time-dependent enhancement of the palmitoyl-CoA synthetase activity both in the mitochondrial, peroxisomal and microsomal fractions. The total carnitine palmitoyltransferase activity in the mitochondrial fraction was enhanced. Ethionine administration was also associated with dose- and time-dependent changes of the microsomal glycerophosphate acyltransferase activity, whereas the mitochondrial enzyme activity was marginally affected. The hepatic triacylglycerol content of the ethionine-treated animals was increased. Hepatic lipids were accumulated in large droplets. Serum triacylglycerol and cholesterol were decreased. In particular, the serum HDL-cholesterol level was lowered. The concentration of ATP in the liver decreased. Accumulation of the metabolic product S-adenosylethionine (AdoEth) was observed for the first 2 days of exposure followed by a fall in S-adenosylmethionine (Ado-Met) during the next 10 days. Linear regression analysis of ATP content versus AdoEth and AdoMet showed highly significant correlations. A significant correlation between the hepatic triacylglycerol and AdoEth content was also observed upon ethionine treatment. The data show that ethionine perturbs the hepatic lipid metabolism. Enhanced esterification of long-chain fatty acids, but not a simple reduction of their oxidation, might contribute to ethionine-induced fatty liver in addition to a block in secretion of lipoproteins and decreased protein synthesis.

Acyltransferases↗

PubMed1988

Pathways of hydrogen peroxide generation in guinea pig cerebral cortex mitochondria.

The production of H2O2 by brain mitochondria was monitored employing a new technique based on the horseradish peroxidase dependent oxidation of acetylated ferrocytochrome c. It was shown that brain mitochondria release H2O2 by an intermediate autooxidation at the QH2-cytochrome c oxidoreductase level (induced by antimycin A and inhibited by myxothiazol). With both succinate and pyruvate plus malate this H2O2 release is inhibited at high substrate concentrations. With pyruvate plus malate a second source of H2O2 could be detected, apparently from autoxidation at the NADH dehydrogenase level. With alpha-glycerophosphate some H2O2 derives from autooxidation at the alpha-glycerophosphate dehydrogenase. The NADH dehydrogenase dependent, but not the QH2-cytochrome c oxidoreductase dependent H2O2 was significantly stimulated upon depletion of the mitochondrial glutathione.

Animals↗

PubMed1985

Biochemical effects of mild iron deficiency and cold acclimatization on rat skeletal muscle.

Most of the previous studies on the effects of iron deficiency on skeletal muscle respiratory capacity and work performance have been investigated in severe or moderate iron-deficiency anemia. We report here that even in mild iron deficiency where the hemoglobin concentration was 10 g/dl and the iron stores in livers and spleen were not completely depleted, a marked reduction in succinate dehydrogenase was observed in skeletal muscles but not in heart. Similarly, cytochrome oxidase activities were reduced. Although no significant change in glycerophosphate dehydrogenase was detected in the iron-deficient rats, exposure to cold in this group greatly reduced this enzyme activity. As cold acclimatization accelerates marrow erythropoiesis (20) which in turn, demands more iron, it seems that in the iron-insufficient state, this iron demand for marrow activity may persist at the expense of the tissue iron pool, resulting in a marked reduction in glycerophosphate dehydrogenase activities. Since succinate dehydrogenase plays a significant role in the impairment of mitochondrial function and early fatigue of iron-deficient muscle (11), the present study shows that even in mild iron deficiency, some loss of muscle functions could result as succinate dehydrogenase activities were greatly reduced.

Acclimatization↗

PubMed1986

Optimization of a vehicle solution for the introduction and removal of glycerol with rabbit kidneys.

Previous studies with rabbit kidneys in our laboratories have used a plasma-like solution as the vehicle for the introduction and removal of glycerol. Other workers have usually employed high-potassium solutions. In this study we have assayed the function of rabbit renal cortical slices after incubation in a range of solutions, each of which contained 1 M glycerol, for 4 hr, followed by stepwise removal of the cryoprotectant. The functions measured were endogenous oxygen consumption, p-aminohippurate uptake, and the ability of the slices to accumulate potassium. Exposure to glycerol produced a considerable reduction of slice function, but, in the presence of glycerol, elevation of the potassium concentration was beneficial, whereas high concentrations of magnesium were detrimental. The optimum potassium concentration was 70-100 mM. Replacement of chloride by a range of anions of higher molecular weight was either without benefit (glycerophosphate) or detrimental (sulfate, citrate, and gluconate). Elevation of total osmolality from 300 to 400 mosmolal with glucose, mannitol, glycerophosphate, or Pipes reduced slice function, but when the same osmolality was achieved by raising the concentration of all the components of the solution in the same ratio, there was no significant loss of function. There was a weak optimum pH at ca. 7.0. These experiments led to the formulation of a bicarbonate-buffered perfusate containing 80 mM potassium and 17.5 g Haemaccel per liter, having a pH of 7.0 with 5% CO2 at 10 degrees C, and an osmolality of 400 mosmol/kg. This solution was used to preserve rabbit kidneys for 20 hr at 10 degrees C, by continuous perfusion, and was compared with our previous Haemaccel perfusate, HP5, which contained 4 mM K+, 111 mM mannitol, and had a pH of 7.4. The two solutions were equally effective.

Animals↗

PubMed1987

De novo CDP-choline-dependent glycerophosphorylcholine synthesis and its involvement as an intermediate in phosphatidylcholine synthesis.

The activity of CDP-choline-dependent glycerophosphorylcholine synthetase (CDP-choline:sn-3-glycerophosphate cholinetransferase), a newly discovered enzyme involved in the recently proposed pathways of acyl-specific phosphatidylcholine synthesis, is reported in rat liver. Endogenous CDP-choline, synthesized via the CMP-driven back reaction of phosphorylcholine transferase, is also shown to be a choline donor for this glycerophosphorylcholine synthetase. The function of glycerophosphorylcholine as an intermediate in phosphatidylcholine synthesis is demonstrated by specific isotope trapping whereby unlabelled glycerophosphorylcholine inhibited label incorporation from sn-[14C]glycerol-3-phosphate into phosphatidylcholine in mouse gastrocnemius, a tissue that is essentially devoid of the cytidine pathway for phosphatidylcholine synthesis and uses a non-allelic glycerophosphorylcholine synthetase (exogenous PC:sn-3-glycerophosphate cholinetransferase) in the synthesis of glycerophosphorylcholine.

Animals↗

PubMed1982

Lactate metabolism and cytosolic NADH reducing equivalents in ovine adipocytes.

1. Isolated ovine adipocytes, unlike rat adipose tissue, could utilize lactate at a high rate. 2. When the rate of fatty acid synthesis was attenuated with 5-(tetradecyloxy)-2-furoic acid, a fatty acid synthesis inhibitor, there was a good positive correlation between the rates of lactate oxidation to CO2 and lactate incorporation into fatty acids. 3. Addition of 2,4-dinitrophenol enhanced lactate oxidation to CO2 independent of fatty acid synthesis. Under this condition, estimated cytosolic NADH formation from lactate dehydrogenation exceeded the need of NADH for cytosolic oxaloacetate reduction and for glyceride glycerol formation. 4. Mitochondria isolated from ovine adipocytes oxidized added NADH rapidly in a reconstituted alpha-glycerophosphate shuttle system. 5. It is possible that the ability of ovine adipocytes to utilize lactate may be related to the active alpha-glycerophosphate shuttle for cytosolic NADH reoxidation.

2,4-Dinitrophenol↗

PubMed1991

Hydrogen peroxide release by mitochondria increases during aging.

The effect of aging on the release of H2O2 by mitochondria was studied in the housefly in order to elucidate the causes of previously observed age-related increase in the level of oxidative stress. Intact flight muscle mitochondria of the housefly, supplemented with alpha-glycerophosphate, produce 1-2 nmol H2O2/min per mg protein, even in the absence of respiratory inhibitors. The rate of H2O2 secretion progressively increases approximately 2-fold during aging of the fly. Neither uncoupling of oxidative phosphorylation nor mechanical damage to mitochondria during the isolation procedure appear to be responsible for the age-related increase in H2O2 production. Activities of NADH-ferricyanide reductase, succinate-ubiquinone reductase, and NADH-, succinate- and alpha-glycerophosphate-cytochrome c reductases, were approximately 2-fold higher in mitochondria from the old than those from the young flies. However, the concentration of enzymatically reducible ubiquinone remained unchanged with age. Infliction of damage by exposure of mitochondria to free radical-generating systems in vitro caused an increase in the rate of H2O2 generation. Glutaraldehyde, an intermolecular crosslinking agent, induced an increase in the rate of H2O2 generation by mitochondria. Results of this study demonstrate that aging in the housefly is associated with an increase in the rate of H2O2 generation by mitochondria probably due, at least in part, to self-inflicted damage by mitochondria. Intermolecular cross-linking in the inner mitochondrial membrane can contribute towards the increased H2O2 generation.

Aging↗

PubMed1983

Occurrence and role of phosphoenolpyruvate carboxykinase in procyclic Trypanosoma brucei brucei glycosomes.

Phosphoenolpyruvate carboxykinase (EC 4.1.1.32) was detected in a particulate fraction of Trypanosoma brucei brucei procyclic culture form. It requires ADP rather than GDP for activity in the direction of carboxylation and is located in the glycosomes. Since phosphoenolpyruvate can serve to furnish ATP for glycolysis and can promote 3-phosphoglycerate or 1,3-bisphosphoglycerate formation without simultaneous alpha-glycerophosphate production, we suggest that the glycosomal phosphoenolpyruvate carboxykinase-malate dehydrogenase tandem contributes to ATP regeneration and NADH re-oxidation in the glycosome, and regulates alpha-glycerophosphate production.

Adenosine Diphosphate↗

PubMed1992

Regulation of mitochondrial glycerol-phosphate dehydrogenase by Ca2+ within electropermeabilized insulin-secreting cells (INS-1).

(1) A new insulin-secreting cell line (INS-1; Asfari et al. (1992) Endocrinology 130, 167-178) has been used to study the regulation by Ca2+ of mitochondrial FAD-linked glycerol-phosphate dehydrogenase (FAD-GPDH) in situ. (2) Enzyme activity was examined on-line in electropermeabilized cells by a new, sensitive, assay. This involved the reduction of the artificial electron acceptor, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT), monitored by the quenching of the fluorescence of rhodamine-18. Using this approach, similar total levels of FAD-GPDH activity (nmol/min per 10(6) cells) were measured in INS-1 cells (1.35 +/- 0.22) and isolated rat islet cells (1.63 +/- 0.02) (3) Ca2+ ions markedly activated the enzyme, lowering the apparent Km-value for added DL-glycerophosphate from 8.8 +/- 1.4 mM to 1.0 +/- 0.1 mM. Ca2+ had no effect on the apparent Vmax. The enzyme displayed cooperative kinetics with respect to DL-glycerophosphate (Hill coefficient of 2.0 +/- 0.2 and 1.6 +/- 0.2 in the absence and presence respectively of Ca2+). Half-maximal effects of Ca2+ were observed in the range 30-130 nM, depending on the concentration of glycerol phosphate. (4) Enzyme activity was weakly (30%) inhibited by diazoxide, but not by the diabetogenic drug, streptozotocin. (5) The data indicate that INS-1 cells represent an excellent model for studying the rôle of FAD-GPDH in the control of insulin secretion.

Animals↗

PubMed1987

Effects of increased energy expenditure on weight gain and adiposity in the LA-corpulent rat.

Groups of lean or pre-obese LA/N-cp rats were subjected to a program of vigorous exercise (less than 4 hr/day) or remained sedentary from 6 weeks until 12 weeks of age. Sedentary pre-obese rats gained weight twice as rapidly as sedentary lean rats. Exercise treatment resulted in greater decrements in body wt in obese than in lean rats, but did not result in absolute weight loss in either group. At 12 weeks of age, fat pad weights in principle depots were 10-15 times greater in corpulent than in lean rats and were significantly smaller in the exercised groups of both phenotypes, and corresponded with lower relative adiposity compared to corresponding sedentary groups. Heart weights were greater in corpulent than lean, while gastrocnemius muscle weights were similar in both phenotypes. Exercise was without effect on the weight of either muscle tissue in either phenotype. Interscapular brown adipose tissue weights and the IBAT:BW ratio were greater in obese than in lean rats. IBAT weights were lower in exercised than sedentary rats of either phenotype, but the IBAT:BW ratio was lower only in the obese exercised rats. In sedentary rats, L-alpha-glycerophosphate dehydrogenase and malic enzyme activity were greater in obese than lean, and exercise treatment resulted in increased L-alpha-glycerophosphate dehydrogenase and malic enzyme only in lean rats. These results are consistent with a redistribution of energy expenditure from energy storing to energy dissipating pathways following vigorous exercise, resulting in slowed rates of weight gain and body fat accretion in both lean and obese animals, with the most significant decrements among pre-obese rats.

Adipose Tissue↗

PubMed1982

Lack of stimulation of renal (Na+ +K+)-ATPase by thyroid hormones in the rabbit.

The effect of 1-3,5,3'-triiodothyronine (T3) and thyroxine (T4) on (Na+ +K+)-ATPase activities was examined in rabbit kidneys because in this tissue almost 80% of the metabolism is connected to active sodium transport. T3-receptor concentrations were estimated as 0.62 and 0.80 pmol/mg per DNA in the cortex and outer medulla, respectively. A dose of 0.5 mg T3/kg body weight for 3 days increased basal metabolic rate by almost 60%, and the mitochondrial 1-alpha-glycerophosphate dehydrogenase activity was increased by 50% in both the cortex and medulla. (Na+ +K+)-ATPase activity in the liver was raised by almost 50%. However, no changes in (Na+ +K+)-ATPase activities or binding sites for [3H]ouabain in either the kidney cortex or medulla could be observed. T4 at 16 mg/kg daily for 14 days was also without effect on renal (Na+ +K+)-ATPase activities. Furthermore, the response to T3 was absent at high sodium excretion rates induced by unilateral nephrectomy and extracellular volume expansion. Thus, despite stimulation of basal metabolic rate and renal 1-alpha-glycerophosphate dehydrogenase activity by T3 and T4, the (Na+ +K+)-ATPase activity in the rabbit kidney is identical in euthyroid and hyperthyroid states. However, thyroid hormones prevent the normal natriuretic response to extracellular volume expansion.

Animals↗

PubMed1979

Hydrogen shuttles in air versus water breathing fishes.

1. The malate-aspartate cycle was demonstrable in subcellular preparations of hearts from Arapaima, Lepidosiren, and Synbranchus (obligate air breathers), Hoplerythriunus (facultative air breather), and Osteoglossum and Hoplias (obligate water breathers). 2. Although no respiratory evidence for significant alpha-glycerophosphate cycle participation could be shown in the air breathers, this cycle was demonstrable in hearts of water breathers. 3. In agreement with the O2 uptake studies, it was possible to reconstruct the malate-aspartate, but not the alpha-glycerophosphate cycle, in isolated mitochondria from air breathers, while both shuttles could be reconstructed with heart mitochondria in the case of water breathing fishes.

Air↗

PubMed1983

Development of rat liver and colon substrate cycle enzymes in offspring with and without prenatal exposure to a carcinogenic dose of 1,2-dimethylhydrazine.

Pregnant F-344 rats were exposed by intubation to a single dose (35 mg/kg) of 1,2-dimethylhydrazine dihydrochloride or to an acetate buffer on day 14 of gestation. A detailed examination of the effects of this dose of 1,2-dimethylhydrazine on brush border enzymes in the offspring was performed. Changes in the liver and colon levels of the alpha-glycerophosphate and malate/aspartate substrate cycle enzymes were measured during the development; at days 17 and 20 of gestation and at 2, 6, 13, 20, 27, 55, 110 days and 1 year after birth. It is concluded that metabolic energy enzymes, glutamate oxaloacetate transaminase and malate dehydrogenase, are more sensitive to 1,2-dimethylhydrazine treatment than are the brush border hydrolases or NAD- and Fp-linked alpha-glycerophosphate dehydrogenases.

1,2-Dimethylhydrazine↗

PubMed1990

A 28 kDa protein of normal mouse serum binds lipopolysaccharides of gram-negative and lipoteichoic acids of gram-positive bacteria.

A 28 kDa protein from normal mouse serum known to bind to the inner core region of bacterial lipopolysaccharide (LPS) was found to bind also to bacterial poly(glycerophosphate) lipoteichoic acid (LTA). Twenty-nine preparations of LTA were isolated from 19 different bacterial species, purified, chemically analysed, and tested for their ability to bind the 28 kDa protein in a complement-dependent hemolysis and hemolysis inhibition assay. All but one were active in one or both systems and one half of the preparations were active in both. Reactivity patterns were not strictly correlated with the chemical structure of LTA considering the substitution of the poly(glycerophosphate) chain with alanine ester and glycosyl residues and the type of lipid anchor. The isolated lipid anchor alone was unable to bind the serum factor. Comparing the binding to LTA and LPS from Acinetobacter calcoaceticus indicated complete cross-reactivity of LTA and LPS in various serological approaches. Thus, LPS and LTA which are unique amphiphiles in Gram-negative and Gram-positive bacteria, respectively, share a similar function in terms of binding the 28 kDa mouse serum protein.

Animals↗

PubMed1995

Activity of cytosolic and mitochondrial enzymes participating in nutrient catabolism of normal and tumoral islet cells.

The aim of the present study is to compare normal and tumoral pancreatic islet cells in terms of both the activity of selected cytosolic and mitochondrial enzymes participating to nutrient catabolism and the intrinsic properties of FAD-glycerophosphate dehydrogenase. The activity of the glycolytic enzymes hexokinase and lactate dehydrogenase was higher in tumoral (RINm5F) than normal islet cells. The opposite was seen for glutamate decarboxylase, glutamate-oxaloacetate transaminase, glutamate-pyruvate transaminase, glutamate dehydrogenase, 2-ketoglutarate dehydrogenase and FAD-glycerophosphate dehydrogenase (m-GDH). These findings are consistent with the high rates of glycolysis and protein synthesis seen in tumoral islet cells compared with normal islet cells, which favour mitochondrial oxidative events associated with the catabolism of D-glucose and amino acids. The intrinsic catalytic properties of m-GDH were comparable, albeit not identical, in normal and tumoral islet cells. Since a deficiency of m-GDH in pancreatic islets may represent a contributing factor in the pathogenesis of non-insulin-dependent diabetes, it is proposed that RINm5F cells may readily yield sufficient islet m-GDH for purification and further gene cloning.

Amino Acids↗

PubMed2006

Phenotype properties of a novel spontaneously immortalized odontoblast-lineage cell line.

Here we report on the spontaneous immortalization upon serial passages of mouse fetal dental papilla cells, which present odontoblast phenotype features. The cells named odontoblast-lineage cell (OLC) produced dentin extracellular matrix proteins, such as DSP and DMP1, and maintained transcripts of various matrix components as osteopontin, BMP-4, procollagen-1, and MEPE. The addition of osteogenic differentiation medium with beta-glycerophosphate and ascorbic acid was effective for inducing calcification and mineralization in vitro in cell cultures for up to 28 days. For the first time, we investigated the expression of Lhx6 and Lhx7 genes during induced biomineralization, since these new members of LIM homeodomain proteins have been recently proposed tracking odontoblastic phenotypes. Our results indicate that beta-glycerophosphate treatment of OLC cultures decreases Lhx6 transcript levels in vitro. Our findings proved odontoblast phenotype-specificity, which demonstrates that this novel odontoblast-lineage cell line is a valuable tool for future experiments in odontology.

Animals↗

PubMed2006

Membrane-bound alkaline phosphatase from ectopic mineralization and rat bone marrow cell culture.

Cells from rat bone marrow exhibit the proliferation-differentiation sequence of osteoblasts, form mineralized extracellular matrix in vitro and release alkaline phosphatase into the medium. Membrane-bound alkaline phosphatase was obtained by method that is easy to reproduce, simpler and fast when compared with the method used to obtain the enzyme from rat osseous plate. The membrane-bound alkaline phosphatase from cultures of rat bone marrow cells has a MW(r) of about 120 kDa and specific PNPP activity of 1200 U/mg. The ecto-enzyme is anchored to the plasma membrane by the GPI anchor and can be released by PIPLC (selective treatment) or polidocanol (0.2 mg/mL protein and 1% (w/v) detergent). The apparent optimum pH for PNPP hydrolysis by the enzyme was pH 10. This fraction hydrolyzes ATP (240 U/mg), ADP (350 U/mg), glucose 1-phosphate (1100 U/mg), glucose 6-phosphate (340 U/mg), fructose 6-phosphate (460 U/mg), pyrophosphate (330 U/mg) and beta-glycerophosphate (600 U/mg). Cooperative effects were observed for the hydrolysis of PPi and beta-glycerophosphate. PNPPase activity was inhibited by 0.1 mM vanadate (46%), 0.1 mM ZnCl2 (68%), 1 mM levamisole (66%), 1 mM arsenate (44%), 10 mM phosphate (21%) and 1 mM theophylline (72%). We report the biochemical characterization of membrane-bound alkaline phosphatase obtained from rat bone marrow cells cultures, using a method that is simple, rapid and easy to reproduce. Its properties are compared with those of rat osseous plate enzyme and revealed that the alkaline phosphatase obtained has some kinetics and structural behaviors with higher levels of enzymatic activity, facilitating the comprehension of the mineralization process and its function.

Alkaline Phosphatase↗

PubMed2003

Activation of peroxisome proliferator-activated receptor-gamma inhibits differentiation of preosteoblasts.

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is critical for phenotype determination at early differentiation stages of mesenchymal cells. Activation of this nuclear receptor inhibits gene expression in part by antagonizing the activities of several transcription factors. In this study we examined inhibitory mechanisms of osteoblast differentiation markers by activating PPAR-gamma. Our data indicate that the PPAR-gamma natural ligand 15d-PGJ2 dose-dependently inhibits expression of alkaline phosphatase and mineral deposition by primary stromal cells and by cell lines such as ST2 and MC3T3-E1. We next show that PPAR-gamma nuclear translocation coincides with duration and doses of ligand addition, indicating that 15d-PGJ2-activated PPAR-gamma rapidly translocates to the nuclear component where it exerts its biological effects. Further examination of downstream osteogenic signaling pathways induced by beta-glycerophosphate and ascorbic acid reveals that induction of osteoblast differentiation by these agents involves activation of the transcription factors Cbfa1 and NF-kappaB. The former is critical for osteoblast differentiation. To test whether inhibition of alkaline phosphatase expression and mineral deposition by activated PPAR-gamma reflects attenuation of transcriptional activity, we performed DNA protein-binding assays for NF-kappaB and Cbfa1. Our findings indicate that 15d-PGJ2-induced PPAR-gamma abrogates beta-glycerophosphate-activated Cbfa1 and NF-kappaB. These findings were consistent in primary and stromal cell lines, ST2 and MC3T3-E1. Thus activation of PPAR-gamma by 15d-PGJ2 inhibits DNA-binding activity of the transcription factors Cbfa1 and NF-kappaB, leading to diminished expression of osteoblast/stromal differentiation markers.

Active Transport, Cell Nucleus↗