Effect of a seaweed extract on fatty acid accumulation and glycerol-3-phosphate dehydrogenase activity in 3T3-L1 adipocytes

This study was to determine the effect of a seaweed Ascophyllum nodosum extract (SE) containing 220 mg g(-1) phlorotannins on differentiation and fatty acid accumulation in differentiating 3T3-L1 adipocytes. 3T3-L1 cells (2 x 10(4) mL(-1)) were seeded to 24-well plates and proliferated to reach confluence and then were treated with media containing 0, 12.5, 25, 50, 75 and 100 mug mL(-1) SE for 8 days. Dexamethasone, methyl-isobutylxanthine and insulin (DMI) were added to the media in the first 2 days to induce cell differentiation. On day 8 the adipocytes were harvested for measuring cellular fatty acid concentration and the activity of glycerol-3-phosphate dehydrogenase (GPDH). It was found that treatment with SE increased (P < 0.01, n = 6) cellular myristoleic acid (C14:1), palmitoleic acid (C16:1) and oleic acid (C18:1) and total monounsaturated fatty acids (MUFA) without significantly affecting the cell number and saturated fatty acid (SFA). Ratios of MUFA/SFA, C14:1/C14:0, C16:1/C16:0 and C18:1/C18:0 in cellular lipids increased (P < 0.05, n = 6) with the SE treatment in a dose dependent manner (P < 0.001). Treatment with 75 microg mL(-1) SE depressed (P < 0.05) cellular GPDH activity. The results indicate that the biological factors in the SE may be involved in differentiation and MUFA accumulation in adipocytes.

Direct evidence that genetic variation in glycerol-3-phosphate and malate dehydrogenase genes (Gpdh and Mdh1) affects adult ethanol tolerance in Drosophila melanogaster

Many studies of alcohol adaptation in Drosophila melanogaster have focused on the Adh polymorphism, yet the metabolic elimination of alcohol should involve many enzymes and pathways. Here we evaluate the effects of glycerol-3-phosphate dehydrogenase (Gpdh) and cytosolic malate dehydrogenase (Mdh1) genotype activity on adult tolerance to ethanol. We have created a set of P-element-excision-derived Gpdh, Mdh1, and Adh alleles that generate a range of activity phenotypes from full to zero activity. Comparisons of paired Gpdh genotypes possessing 10 and 60% normal activity and 66 and 100% normal activity show significant effects where higher activity increases tolerance. Mdh1 null allele homozygotes show reductions in tolerance. We use piggyBac FLP-FRT site-specific recombination to create deletions and duplications of Gpdh. Duplications show an increase of 50% in activity and an increase of adult tolerance to ethanol exposure. These studies show that the molecular polymorphism associated with GPDH activity could be maintained in natural populations by selection related to adaptation to alcohols. Finally, we examine the interactions between activity genotypes for Gpdh, Mdh1, and Adh. We find no significant interlocus interactions. Observations on Mdh1 in both Gpdh and Adh backgrounds demonstrate significant increases in ethanol tolerance with partial reductions (50%) in cytosolic MDH activity. This observation strongly suggests the operation of pyruvate-malate and, in particular, pyruvate-citrate cycling in adaptation to alcohol exposure. We propose that an understanding of the evolution of tolerance to alcohols will require a system-level approach, rather than a focus on single enzymes.

Isorhamnetin represses adipogenesis in 3T3-L1 cells

Adipocyte dysfunction is strongly associated with the development of obesity, which is a major risk factor for many disorders including diabetes, hypertension, and heart disease. It is generally accepted that the regulation of adipogenesis or adipokines expression prevents obesity. In this study, we show that isorhamnetin inhibits adipocyte differentiation, as evidenced by reduced triglyceride (TG) accumulation and glycerol-3-phosphate dehydrogenase (GPDH) activity. At the molecular level, the mRNA expression levels of peroxidase proliferator-activated receptor-gamma (PPAR-gamma) and CCAAT/enhancer-binding protein-alpha (C/EBP-alpha), which are the major adipogenic transcription factors, were markedly reduced by isorhamnetin. However, the mRNA levels of C/EBP-beta and -delta, the upstream regulators of PPAR-gamma and C/EBP-alpha, were not reduced by isorhamnetin. Moreover, the mRNA levels of PPAR-gamma target genes such as lipoprotein lipase (LPL), CD36, aP2, and liver X receptor-alpha (LXR-alpha) were downregulated by isorhamnetin. We also showed that isorhamnetin inhibits the expression and secretion of adiponectin, and the results of adiponectin promoter assays suggest the inhibition of PPAR-gamma expression as a possible mechanism underlying the isorhamnetin-mediated effects. Taken together, these results indicate that isorhamnetin inhibits adipogenesis through downregulation of PPAR-gamma and C/EBP-alpha.

[Characterization of glycerol-3-phosphate dehydrogenase gene (CgGPD) from the glycerol producing Candida glycerinogenes]

OBJECTIVE

Candida glycerinogenes, an excellent glycerol producer, has been used for commercial scale glycerol production. Recently, we cloned and sequenced the gene encoding NAD+-dependent glycerol 3-phosphate dehydrogenase (GPD) from C. glycerinogenes and this gene was named CgGPD, which plays an important role in glycerol production. However, compared with GPD1 and GPD2 from S. cerevisiae, the function of CgGPD was unclear to date.

METHODS

In this study, a functional charaterization of CgGPD was undertaken, using S. cerevisiae and its isogenic gpd1/gpd2 mutant as expression host under high osmotic stress.

RESULTS

Expression of CgGPD in wide type S. cerevisiae, using either TPI promoter from S. cerevisiae or upstream regulatory sequence of CgGPD accelerated glucose consumption rate and improved glycerol production signifcantly. In osmosensitive mutant, expresion of CgGPD including regulatory sequence increased cells osmotic tolernace and growth profile of transformants restored similar to wide type strain under the high osmotic stress condition. Furthermore, mutants harbouring CgGPD accumulated the intracellular glycerol content markedly and GPD specific enzyme activity increased abruptly when exposed to high osmolarity medium.

CONCLUSION

CgGPD from C. glycerinogenes compensate the GPD1 in S. cerevisiae functionally.

Regulation of proliferation and differentiation of adipocyte precursor cells in rainbow trout (Oncorhynchus mykiss)

Here, we describe optimal conditions for the culture of rainbow trout (Oncorhynchus mykiss) pre-adipocytes obtained from adipose tissue and their differentiation into mature adipocytes, in order to study the endocrine control of adipogenesis. Pre-adipocytes were isolated by collagenase digestion and cultured on laminin or 1% gelatin substrate. The expression of proliferating cell nuclear antigen was used as a marker of cell proliferation on various days of culture. Insulin growth factor-I stimulated cell proliferation especially on days 5 and 7 of culture. Tumor necrosis factor alpha (TNFalpha) slightly enhanced cell proliferation only at a low dose. We verified the differentiation of cells grown in specific medium into mature adipocytes by oil red O (ORO) staining. Quantification of ORO showed an increase in triglycerides throughout culture. Immunofluorescence staining of cells at day 11 revealed the expression of CCAAT/enhancer-binding protein and peroxisome proliferator-activator receptor gamma, suggesting that these transcriptional factors are involved in adipocyte differentiation in trout. We also examined the effect of TNFalpha on the differentiation of these adipocytes in primary culture. TNFalpha inhibited the differentiation of these cells, as indicated by a decrease in glycerol-3-phosphate dehydrogenase activity, an established marker of adipocyte differentiation. In conclusion, the culture system described here for trout pre-adipocytes is a powerful tool to study the endocrine regulation of adipogenesis in this species.

Prolactin inhibition at the end of lactation programs for a central hypothyroidism in adult rat

Malnutrition during lactation is associated with hypoprolactinemia and failure in milk production. Adult rats whose mothers were malnourished presented higher body weight and serum tri-iodothyronine (T(3)). Maternal hypoprolactinemia at the end of lactation caused higher body weight in adult life, suggesting an association between maternal prolactin (PRL) level and programming of the offspring's adult body weight. Here, we studied the consequences of the maternal PRL inhibition at the end of lactation by bromocriptine (BRO) injection, a dopaminergic agonist, upon serum TSH and thyroid hormones, thyroid iodide uptake, liver mitochondrial alpha-glycerophosphate dehydrogenase (mGPD), liver and pituitary de-iodinase activities (D1 and/or D2), and in vitro post-TRH TSH release in the adult offspring. Wistar lactating rats were divided into BRO - injected with 1 mg/twice a day, daily for the last 3 days of lactation, and C - control, saline-injected with the same frequency. At 180 days of age, the offspring were injected with (125)I i.p. and after 2 h, they were killed. Adult animals whose mothers were treated with BRO at the end of lactation presented lower serum TSH (-51%), T(3) (-23%), and thyroxine (-21%), lower thyroid (125)I uptake (-41%), liver mGPD (-55%), and pituitary D2 (-51%) activities, without changes in the in vitro post-TRH TSH release. We show that maternal PRL suppression at the end of lactation programs a hypometabolic state in adulthood, in part due to a thyroid hypofunction, caused by a central hypothyroidism, probably due to decreased TRH secretion. We suggest that PRL during lactation can regulate the hypothalamus-pituitary-thyroid axis and programs its function.

Glycerol-3-phosphate levels are associated with basal resistance to the hemibiotrophic fungus Colletotrichum higginsianum in Arabidopsis

Glycerol-3-phosphate (G3P) is an important component of carbohydrate and lipid metabolic processes. In this article, we provide evidence that G3P levels in plants are associated with defense to a hemibiotrophic fungal pathogen Colletotrichum higginsianum. Inoculation of Arabidopsis (Arabidopsis thaliana) with C. higginsianum was correlated with an increase in G3P levels and a concomitant decrease in glycerol levels in the host. Plants impaired in utilization of plastidial G3P (act1) accumulated elevated levels of pathogen-induced G3P and displayed enhanced resistance. Furthermore, overexpression of the host GLY1 gene, which encodes a G3P dehydrogenase (G3Pdh), conferred enhanced resistance. In contrast, the gly1 mutant accumulated reduced levels of G3P after pathogen inoculation and showed enhanced susceptibility to C. higginsianum. Unlike gly1, a mutation in a cytosolic isoform of G3Pdh did not alter basal resistance to C. higginsianum. Furthermore, act1 gly1 double-mutant plants were as susceptible as the gly1 plants. Increased resistance or susceptibility of act1 and gly1 plants to C. higginsianum, respectively, was not due to effects of these mutations on salicylic acid- or ethylene-mediated defense pathways. The act1 mutation restored a wild-type-like response in camalexin-deficient pad3 plants, which were hypersusceptible to C. higginsianum. These data suggest that G3P-associated resistance to C. higginsianum occurs independently or downstream of the camalexin pathway. Together, these results suggest a novel and specific link between G3P metabolism and plant defense.

Polychlorinated biphenyl-77 induces adipocyte differentiation and proinflammatory adipokines and promotes obesity and atherosclerosis

BACKGROUND

Obesity, an inflammatory condition linked to cardiovascular disease, is associated with expansion of adipose tissue. Highly prevalent coplanar polychlorinated biphenyls (PCBs) such as 3,3',4,4'-tetrachlorobiphenyl (PCB-77) accumulate in adipose tissue because of their lipophilicity and increase with obesity. However, the effects of PCBs on adipocytes, obesity, and obesity-associated cardiovascular disease are unknown.

OBJECTIVES

In this study we examined in vitro and in vivo effects of PCB-77 on adipocyte differentiation, proinflammatory adipokines, adipocyte morphology, body weight, serum lipids, and atherosclerosis.

METHODS

PCB-77 or 2,2',4,4,5,5'-hexachlorobiphenyl (PCB-153) was incubated with 3T3-L1 adipocytes either during differentiation or in mature adipocytes. Concentration-dependent effects of PCB-77 were contrasted with those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). For in vivo studies, we treated C57BL/6 wild-type (WT) or aryl hydrocarbon receptor (AhR)(-/-) mice with vehicle or PCB-77 (49 mg/kg, by intraperitoneal injection) and examined body weight gain. In separate studies, we injected ApoE(-/-) mice with vehicle or PCB-77 over a 6-week period and examined body weight, adipocyte size, serum lipids, and atherosclerosis.

RESULTS

Low concentrations of PCB-77 or TCDD increased adipocyte differentiation, glycerol-3-phosphate dehydrogenase activity, and expression of peroxisome proliferator-activated receptor gamma, whereas higher concentrations inhibited adipocyte differentiation. Effects of PCB-77 were abolished by the AhR antagonist alpha-naphthoflavone. PCB-77 promoted the expression and release of various proinflammatory cytokines from 3T3-L1 adipocytes. Administration of PCB-77 increased body weight gain in WT but not AhR(-/-) mice. ApoE(-/-) mice injected with PCB-77 exhibited greater body weight, adipocyte hypertrophy, serum dyslipidemia, and augmented atherosclerosis.

CONCLUSIONS

Our findings suggest that PCB-77 may contribute to the development of obesity and obesity-associated atherosclerosis.

Plastid omega3-fatty acid desaturase-dependent accumulation of a systemic acquired resistance inducing activity in petiole exudates of Arabidopsis thaliana is independent of jasmonic acid

Systemic acquired resistance (SAR) is an inducible defense mechanism that is activated throughout the plant, subsequent to localized inoculation with a pathogen. The establishment of SAR requires translocation of an unknown signal from the pathogen-inoculated leaf to the distal organs, where salicylic acid-dependent defenses are activated. We demonstrate here that petiole exudates (PeXs) collected from Arabidopsis leaves inoculated with an avirulent (Avr) Pseudomonas syringae strain promote resistance when applied to Arabidopsis, tomato (Lycopersicum esculentum) and wheat (Triticum aestivum). Arabidopsis FATTY ACID DESATURASE7 (FAD7), SUPPRESSOR OF FATTY ACID DESATURASE DEFICIENCY1 (SFD1) and SFD2 genes are required for accumulation of the SAR-inducing activity. In contrast to Avr PeX from wild-type plants, Avr PeXs from fad7, sfd1 and sfd2 mutants were unable to activate SAR when applied to wild-type plants. However, the SAR-inducing activity was reconstituted by mixing Avr PeXs collected from fad7 and sfd1 with Avr PeX from the SAR-deficient dir1 mutant. Since FAD7, SFD1 and SFD2 are involved in plastid glycerolipid biosynthesis and SAR is also compromised in the Arabidopsis monogalactosyldiacylglycerol synthase1 mutant we suggest that a plastid glycerolipid-dependent factor is required in Avr PeX along with the DIR1-encoded lipid transfer protein for long-distance signaling in SAR. FAD7-synthesized lipids provide fatty acids for synthesis of jasmonic acid (JA). However, co-infiltration of JA and methylJA with Avr PeX from fad7 and sfd1 did not reconstitute the SAR-inducing activity. In addition, JA did not co-purify with the SAR-inducing activity confirming that JA is not the mobile signal in SAR.

Co-immobilization of lipase, glycerol kinase, glycerol-3-phosphate oxidase and peroxidase on to aryl amine glass beads affixed on plastic strip for determination of triglycerides in serum

Commercial lipase, glycerol kinase (GK), glycerol-3-phosphate oxidase (GPO) and peroxidase (POD) have been co-immobilized covalently on to arylamine glass beads affixed on a plastic strip through diazotization with a conjugation yield of 89.1 mg/g support and 64.1% retention of specific activity. The co-immobilized enzymes showed maximum activity at pH 7.5, when incubated at 40 degrees C for 20 min. The strip was employed for determination of serum triglycerides (Tgs). The minimum detection limit of the method was 0.20 mM/L. The recovery of added Tgs was 88.0%. Within day and between day coefficient of variations were <7.0 % and <11.0%, respectively. A good correlation (r = 0.982) was observed between total serum Tgs values obtained by present method and the most commonly used enzymic colorimetric method, employing free enzymes. Among the various serum substances tested at their physiological concentrations, only cholesterol, ascorbic acid and bilirubin caused 30%, 15%, and 20% inhibition of strip-bound enzymes, respectively. The strip lost 50% of its activity after 150 regular uses over a period of 33 days, when stored in reaction buffer at 4 degrees C. The method reported here has the advantage over other existing methods, as it provides higher sensitivity, better stability and reusability of co-immobilized enzymes and is also economical.

Coupling kinetic expressions and metabolic networks for predicting wine fermentations

Problematic fermentations are commonplace and cause wine industry producers substantial economic losses through wasted tank capacity and low value final products. Being able to predict such fermentations would enable enologists to take preventive actions. In this study we modeled sugar uptake kinetics and coupled them to a previously developed stoichiometric model, which describes the anaerobic metabolism of Saccharomyces cerevisiae. The resulting model was used to predict normal and slow fermentations under winemaking conditions. The effects of fermentation temperature and initial nitrogen concentration were modeled through an efficiency factor incorporated into the sugar uptake expressions. The model required few initial parameters to successfully reproduce glucose, fructose, and ethanol profiles of laboratory and industrial fermentations. Glycerol and biomass profiles were successfully predicted in nitrogen rich cultures. The time normal or slow wine fermentations needed to complete the process was predicted accurately, at different temperatures. Simulations with a model representing a genetically modified yeast fermentation, reproduced qualitatively well literature results regarding the formation of minor compounds involved in wine complexity and aroma. Therefore, the model also proves useful to explore the effects of genetic modifications on fermentation profiles.

Porcine preadipocyte proliferation and differentiation: a role for leptin?

The present study was designed to determine whether porcine leptin can alter the proliferation and differentiation of the porcine preadipocyte. The stromal vascular cell fraction of neonatal pig s.c. adipose tissue was isolated by collagenase digestion, filtration, and subsequent centrifugation. For differentiation studies, cells were seeded on six-well tissue culture plates and proliferated to confluency in 10% (vol/vol) fetal bovine serum (FBS) in Dulbecco's modified Eagle medium/F12 (DMEM/F12; 50:50). Cultures were differentiated using 2.5% pig serum (vol/vol) and recombinant porcine leptin at concentrations of 0 to 1,000 ng/mL alone or in combination with porcine insulin (100 nM), dexamethasone (1 microM), or IGF-1 (250 ng/mL). After 7 d of lipid filling, cultures were harvested for analysis of sn-glycerol 3 phosphate dehydrogenase (GPDH) and lipoprotein lipase (LPL). The GPDH and LPL activities are measures of preadipocyte differentiation. Data were corrected for protein content of the cultures. For proliferation experiments, 24 h after seeding cells with 10% FBS in DMEM/F12 in 25-cm2 tissue culture flasks, cells were switched to 5% FBS and supplemented with 0 to 1,000 ng of porcine leptin or 1,000 ng of murine leptin. Cell proliferation was measured by 3H-thymidine incorporation in preconfluent cultures over 24 h on d 4 of culture. At confluency, cells were switched to a medium to promote differentiation and lipid filling (2.5% pig serum, 100 nM insulin, 1 microM dexamethasone) for 7 d. Cells were harvested from the flasks and adipocytes were separated from stromal cells by Percoll gradient centrifugation. In a series of experiments, leptin alone or in combination with insulin, dexamethasone, or IGF-I did not affect differentiation as measured by the activity of GPDH and LPL. Leptin at any concentration did not inhibit differentiation induced by insulin, dexamethasone, or IGF-I; however, leptin at 1,000 ng/mL stimulated a 30% increase in preadipocyte proliferation (P = 0.007; n = 6) and a 27% increase in stromal cell proliferation (P < 0.001; n = 6). These results indicate that, at most, porcine leptin may contribute to the recruitment of new adipocytes within the adipose tissue.

Thyroid function and body weight programming by neonatal hyperthyroidism in rats - the role of leptin and deiodinase activities

Several authors have shown that secondary hypothyroidism was programed by neonatal thyroxine (T4) treatment. However, the associated changes of body weight (BW) were less studied, especially those related to the body fat proportion. Here, we have evaluated the effect of neonatal thyroxine treatment on BW, fat proportion, serum leptin, and thyroid function of 60-day-old rats. Wistar rats were treated with thyroxine (50 microg/100 g BW, ip) (T) or saline (S), during the first 10 days of life. BW, nose-rump length (NRL), and food consumption were monitored for 60 days, when the animals were sacrificed. Thyroid function was evaluated by thyroid radioiodine uptake (RAIU), serum T3, T4, TSH, and liver mitochondrial alpha-glycerophosphate dehydrogenase (mGPD) and type 1 and 2 deiodinases (D1 and D2) activities, which are thyroid hormone-dependent enzymes. T animals showed lower food intake, BW and NRL, but higher total fat mass (+33%) and serum leptin (+46%). They also showed lower serum T3 (-23%), T4 (-32%), TSH (-36%), RAIU (-29%) and mGPD activity (-22%). Hypothalamic and pituitary D2 activities were higher (+24% and 1.4 fold, respectively), while brown adipose tissue (BAT) D2 and skeletal muscle D1 activities were lower (-30% and -62%, respectively). Thus, neonatal hyperthyroidism programs for a higher fat proportion and hyperleptinemia, which can explain the lower food intake. The TH-dependent enzymes activities changed accordingly, except for the decrease in BAT D2, which may be due the role played by the hyperleptinemia. Finally, the decrease in peripheral deiodination may contribute to a lower me-tabolic rate that may increase the adiposity.

Cytotoxicity of Mycoplasma mycoides subsp. mycoides small colony type to bovine epithelial cells

The cytotoxicities of various strains of Mycoplasma mycoides subsp. mycoides small colony type (SC), the agent of contagious bovine pleuropneumonia (CBPP), were measured in vitro using embryonic calf nasal epithelial (ECaNEp) cells. Strains isolated from acute cases of CBPP induced high cytotoxicity in the presence of glycerol, concomitant with the release of large amounts of toxic H2O2 that were found to be translocated into the cytoplasms of the host cells by close contact of the Mycoplasma strains with the host cells. Currently used vaccine strains also showed high cytotoxicity and high H2O2 release, indicating that they are attenuated in another virulence attribute. Strains isolated from recent European outbreaks of CBPP with mild clinical signs, which are characterized by a defect in the glycerol uptake system, released small amounts of H2O2 and showed low cytotoxicity to ECaNEp cells. M. mycoides subsp. mycoides SC strain PG1 released large amounts of H2O2 but was only slightly cytotoxic. PG1 was found to have a reduced capacity to bind to ECaNEp cells and was unable to translocate H2O2 into the bovine cells, in contrast to virulent strains that release large amounts of H2O2. Thus, an efficient translocation of H2O2 into host cells is a prerequisite for the cytotoxic effect and requires an intact adhesion mechanism to ensure a close contact between mycoplasmas and host cells.

Gymnemic acid interacts with mammalian glycerol-3-phosphate dehydrogenase

In a previous study, we found interaction of gymnemic acid (GA) with glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key enzyme in glycolysis. We now examined interaction of GA with glycolytic and related enzymes. We found that (1) GA induced a band smearing of glycerol-3-phosphate dehydrogenase (G3PDH) as well as that of GAPDH in SDS-PAGE, (2) GA diminished the G3PDH band detected by an antibody to phosphoserine, and (3) GA inhibited the G3PDH activity. The GA-induced smearing of the G3PDH band was diminished by prior incubation of GA with gamma-cyclodextrin. GA gave no effects on the electrophoretic and phosphoserine bands of other glycolytic enzymes. NAD and NADH diminished the GA-induced smearing of the G3PDH and GAPDH bands in different concentration-dependent manner. Pretreatment of G3PDH with heated SDS-containing buffer or pretreatment with hydroxylamine diminished the GA-induced smearing of G3PDH. Deacylation of GA by alkaline hydrolysis diminished the smearing of G3PDH band, thereby indicating that the acyl moieties of GA were necessary for the GA-induced smearing of G3PDH. These results indicated the interaction of GA with G3PDH, an enzyme involved in glycerol metabolism. These studies suggest that GA may have some pharmacological activities including antidiabetic activity and lipid lowering effects via interaction with GAPDH and G3PDH.

Stimulation of H2O2 generation by calcium in brain mitochondria respiring on α-glycerophosphate

It has been reported recently (Tretter et al., 2007b) that in isolated guinea pig brain mitochondria supported by alpha-glycerophosphate (alpha-GP) reactive oxygen species (ROS) are produced through the reverse electron transport (RET) in the respiratory chain and by alpha-glycerophosphate dehydrogenase (alpha-GPDH). We studied the effect of calcium on the generation of H(2)O(2) as measured by the Amplex Red fluorescent assay in this model. H(2)O(2) production in alpha-GP-supported mitochondria was increased significantly in the presence of 100, 250, and 500 nM Ca(2+), respectively. In addition, Ca(2+) enhanced the membrane potential, the rate of oxygen consumption, and the NAD(P)H autofluorescence in these mitochondria. Direct measurement of alpha-GPDH activity showed that Ca(2+) stimulated the enzyme by decreasing the Km for alpha-GP. In those mitochondria where RET was eliminated by the Complex I inhibitor rotenone (2 microM) or due to depolarization by ADP (1 mM), the rate of H(2)O(2) formation was smaller and the stimulation of H(2)O(2) generation by Ca(2+) was prevented partly, but the stimulatory effect of Ca(2+) was still significant. These data indicate that in alpha-GP-supported mitochondria activation of alpha-GPDH by Ca(2+) leads to an accelerated RET-mediated ROS generation as well as to a stimulated ROS production by alpha-GPDH.

Cold exposure restores the decrease in leptin receptors (OB-Rb) caused by neonatal leptin treatment in 30-day-old rats

We had previously shown that neonatal leptin treatment programs thyroid function in adulthood. As both thyroid hormones (TH) and leptin increased thermogenesis, it was interesting to evaluate the effect of cold exposure on the thyroid function of neonate rats treated with leptin. Pups were divided into two groups: Lep, injected with leptin (8 mug/100 g/BW, s.c.) for the first 10 days of lactation and control (C), injected with saline. When they were 30 days old, the groups were subdivided into two subgroups: LepC and CC, which were exposed to 8 degrees C for 12 h and compared with C and Lep groups, maintained at 25 +/- 1 degrees C. Serum leptin, TH, and TSH were measured by RIA. Type I liver deiodinase (D1) and mitochondrial alpha-glycerol-3-phosphate dehydrogenase (mGPD) activities were assayed by the release of (125)I from (125)I-reverse and colorimetric method respectively. Leptin receptor (OB-Rb) was evaluated by western blot. Lep group had hyperleptinemia (+22%) and lower free tri-iodothyronine (FT(3); -33%). Cold exposure increased TH both in LepC and CC groups compared with respective controls free thyroxine (FT(4):+63 and +39%; FT(3):+75 and +40%). Liver D1 activity was lower in Lep (-22%) and increased with cold exposure (LepC +51% and CC +22%). The mGPD activity was lower in Lep (-34%) and increased (fourfold) when this group is cold exposed. Hypothalamic and thyroidal OB-Rb receptors were lower in Lep group (-47 and -36% respectively) and they were restored to normal levels after cold exposure. Leptin-programmed rats had higher TH response after cold exposure. OB-Rb had a fast response to cold exposure normalizing the lower levels observed in the leptin-programmed animals and may contribute to the higher TH cold responses.

Levels of plasma insulin, leptin and adiponectin, and activities of key enzymes in carbohydrate metabolism in skeletal muscle and liver in fasted ICR mice fed dietary n-3 polyunsaturated fatty acids

The aim of this study was to clarify the mechanisms related to plasma glucose concentration in mice fed a diet rich in n-3 polyunsaturated fatty acids (n-3 PUFAs). Male Crlj:CD-1 (ICR) mice were fed experimental diets containing 6% lard (LD), 6% fish oil (FO) or 4.1% lard plus 1.5% docosahexaenoic acid ethyl ester and 0.4% eicosapentaenoic acid ethyl ester (DE) for 12 weeks. There were no marked differences in plasma glucose and insulin concentration changes on glucose tolerance test between the three dietary groups. At the end of the feeding trial, plasma glucose concentration was significantly lower in fasted mice in the FO group than in those in the LD group (P<.005). Plasma adiponectin concentration was significantly higher in the FO group than in the LD group (P<.05). Hexokinase, phosphofructokinase, glucose-6-phosphate dehydrogenase and glycerophosphate dehydrogenase activities in skeletal muscle tended to be lower in the FO group than in the LD group, while there were no differences in glucokinase and phosphofructokinase activities in liver between the three dietary groups. However, hepatic glycerophosphate dehydrogenase activity was 53-fold and 4.2-fold higher in the FO group than in the LD and DE groups, respectively (P<.0005 and P<.05, respectively). These results suggest that the reduction in plasma glucose concentration in mice fed n-3 PUFAs is mainly caused by acceleration of glucose uptake and glycerol synthesis in the liver rather than in the skeletal muscle.

Follistatin rescues the inhibitory effect of activin A on the differentiation of bovine preadipocyte

We investigated the effect of activin A and follistatin on the differentiation of bovine preadipocytes. Stromal-vascular (SV) cells containing preadipocytes were prepared from perirenal adipose tissue of approximately 30-month-old Japanese Black steers. After confluence, differentiation was induced by 1-methyl-3-isobutyl-xanthine, dexamethasone, insulin and troglitasone for 2 days, and then subsequently cultured for 6 days. The cells were treated with activin A during the induction of differentiation (the early phase of differentiation) or throughout the differentiation period. We measured the terminal differentiation markers such as glycerol-3-phosphate dehydrogenase (GPDH) activity, lipid accumulation, and the expression of adipocyte fatty acid-binding protein mRNA at the end of cultures. Activin A suppressed the induction of all differentiation markers regardless of the duration of treatment. The treatment with activin A also reduced the expression of peroxisome proliferator-activated receptor (PPAR) gamma and CCAAT/enhancer binding protein (C/EBP) alpha mRNAs without affecting the expression of C/EBPbeta mRNA. We also observed that follistatin completely rescued the inhibitory effect of activin A on bovine preadipocyte differentiation. Furthermore, the higher doses of follistatin increased GPDH activity even in the presence of activin A compared with the cells treated with neither activin A nor follistatin. Additionally, the SV cells expressed activin A and myostatin mRNAs. These results suggest that activin A inhibits bovine preadiopocyte differentiation via affecting transcriptional cascade upstream of PPARgamma and C/EBPalpha expressions, and that follistatin suppresses the inhibitory effect of activin A on bovine preadipocyte differentiation. Endogenous activin A and/or myostatin possibly inhibit the differentiation of bovine preadipocytes.

In vitro effects of chorionic gonadotropin hormone on human adipose development

It is well known that pregnancy is associated with fat weight gain. However, the mechanisms whereby fat mass accumulation is controlled during this period are poorly understood. Therefore, we attempted to determine whether human chorionic gonadotropin (HCG), in vitro, influences human adipose tissue development and/or metabolism. For the first time, HCG/LH receptor was characterized in human adipose cells. We also demonstrated that physiological concentrations of HCG, while unaltering both lipolysis and expression of two markers of lipogenesis (FAS and ADD1) in human mature adipocytes, stimulate human preadipocyte growth via the activation of a protein kinase A-independent mitogen-activated protein kinase/c-fos signaling pathway. HCG also moderately increases the preadipocyte differentiation capacity as reflected by enhanced glycerophosphate dehydrogenase activity and expression of key adipogenic transcriptional factors (C/enhancer-binding protein alpha and peroxisome proliferator-activated receptor gamma 2). Finally, HCG significantly stimulates the secretion of the pro-adipogenic factor, leptin, from human adipose tissue. Taken altogether, these data suggest that the pro-adipogenic effect of HCG in human preadipocytes contributes to explain why increased fat storage occurs during the first trimester of pregnancy.

Respiratory chain components involved in the glycerophosphate dehydrogenase-dependent ROS production by brown adipose tissue mitochondria

Involvement of mammalian mitochondrial glycerophosphate dehydrogenase (mGPDH, EC 1.1.99.5) in reactive oxygen species (ROS) generation was studied in brown adipose tissue mitochondria by different spectroscopic techniques. Spectrofluorometry using ROS-sensitive probes CM-H2DCFDA and Amplex Red was used to determine the glycerophosphate- or succinate-dependent ROS production in mitochondria supplemented with respiratory chain inhibitors antimycin A and myxothiazol. In case of glycerophosphate oxidation, most of the ROS originated directly from mGPDH and coenzyme Q while complex III was a typical site of ROS production in succinate oxidation. Glycerophosphate-dependent ROS production monitored by KCN-insensitive oxygen consumption was highly activated by one-electron acceptor ferricyanide, whereas succinate-dependent ROS production was unaffected. In addition, superoxide anion radical was detected as a mGPDH-related primary ROS species by fluorescent probe dihydroethidium, as well as by electron paramagnetic resonance (EPR) spectroscopy with DMPO spin trap. Altogether, the data obtained demonstrate pronounced differences in the mechanism of ROS production originating from oxidation of glycerophosphate and succinate indicating that electron transfer from mGPDH to coenzyme Q is highly prone to electron leak and superoxide generation.

Effects of intensity and duration of exercise on muscular responses to training of thoroughbred racehorses

This study examined the effects of the intensity and duration of exercise on the nature and magnitude of training adaptations in muscle of adolescent (2–3 yr old) racehorses. Six thoroughbreds that had been pretrained for 2 mo performed six consecutive conditioning programs of varying lactate-guided intensities [velocities eliciting blood lactate concentrations of 2.5 mmol/l (v2.5) and 4 mmol/l (v4), respectively] and durations (5, 15, 25 min). Pre- and posttraining gluteus muscle biopsies were analyzed for myosin heavy chain content, fiber-type composition, fiber size, capillarization, and fiber histochemical oxidative and glycolytic capabilities. Although training adaptations were similar in nature, they varied greatly in magnitude among the different training protocols. Overall, the use of v4 as the exercise intensity for 25 min elicited the most consistent training adaptations in muscle, whereas the minimal training stimulus that evoked any significant change was identified with exercises of 15 min at v2.5. Within this range, muscular adaptations showed significant trends to be proportional to the exercise load of specific training programs. Taken together, these data suggest that muscular adaptations to training in horses occur on a continuum that is based on the exercise intensity and duration of training. The practical implications of this study are that exercises for 15 to 25 min/day at velocities between v2.5 and v4 can improve in the short term (3 wk) the muscular stamina in thoroughbreds. However, exercises of 5–15 min at v4 are necessary to enhance muscular features related to strength (hypertrophy).

Increasing seed oil content in oil-seed rape (Brassica napus L.) by over-expression of a yeast glycerol-3-phosphate dehydrogenase under the control of a seed-specific promoter

Previous attempts to manipulate oil synthesis in plants have mainly concentrated on the genes involved in the biosynthesis and use of fatty acids, neglecting the possible role of glycerol-3-phosphate supply on the rate of triacylglycerol synthesis. In this study, a yeast gene coding for cytosolic glycerol-3-phosphate dehydrogenase (gpd1) was expressed in transgenic oil-seed rape under the control of the seed-specific napin promoter. It was found that a twofold increase in glycerol-3-phosphate dehydrogenase activity led to a three- to fourfold increase in the level of glycerol-3-phosphate in developing seeds, resulting in a 40% increase in the final lipid content of the seed, with the protein content remaining substantially unchanged. This was accompanied by a decrease in the glycolytic intermediate dihydroxyacetone phosphate, the direct precursor of glycerol-3-phosphate dehydrogenase. The levels of sucrose and various metabolites in the pathway from sucrose to fatty acids remained unaltered. The results show that glycerol-3-phosphate supply co-limits oil accumulation in developing seeds. This has important implications for strategies that aim to increase the overall level of oil in commercial oil-seed crops for use as a renewable alternative to petrol.

Myosin heavy chain isoform transitions in canine skeletal muscles during postnatal growth

To gain a better understanding of the normal characteristics of developing canine muscles, myosin heavy chain (MHC) isoform expression was analysed in the axial and limb skeletal muscles of 18 young dogs whose ages ranged from the late prenatal stage to 6 months. We compared the results of immunohistochemistry using ten monoclonal antibodies, specific to different MHC isoforms, and enzyme-histochemical reactions, which demonstrate the activity of myofibrillar ATPase, succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (alpha-GPDH). In the skeletal muscles of fetuses and neonatal dogs the developmental isoforms MHC-emb and MHC-neo were prevalent. In all muscles the primary fibres, located centrally in each muscle fascicle, strongly expressed the slow isoform MHC-I. The adult fast isoform MHC-IIa was first noted in some of the secondary fibres on fetal day 55. During the first 10 days after birth, the expression of MHC-emb declined, as did that of MHC-neo during the second and third weeks. Correspondingly, the expression of MHC-IIa, and later, of MHC-I increased in the secondary fibres. Between the sixth week and second month the expression of MHC-IIx became prominent. The slow rhomboideus muscle exhibited an early expression of the slow isoform in the secondary fibres. Our results indicate that the timing of muscle maturation depends on its activity immediately following birth. The fastest developing muscle was the diaphragm, followed by the fast muscles. A pronounced changeover from developmental to adult isoforms was noted at 4-6 weeks of age, which coincides with the increased physical activity of puppies.

Evidence for a higher glycolytic than oxidative metabolic activity in white matter of rat brain

Different values exist for glucose metabolism in white matter; it appears higher when measured as accumulation of 2-deoxyglucose than when measured as formation of glutamate from isotopically labeled glucose, possibly because the two methods reflect glycolytic and tricarboxylic acid (TCA) cycle activities, respectively. We compared glycolytic and TCA cycle activity in rat white structures (corpus callosum, fimbria, and optic nerve) to activities in parietal cortex, which has a tight glycolytic-oxidative coupling. White structures had an uptake of [(3)H]2-deoxyglucose in vivo and activities of hexokinase, glucose-6-phosphate isomerase, and lactate dehydrogenase that were 40-50% of values in parietal cortex. In contrast, formation of aspartate from [U-(14)C]glucose in awake rats (which reflects the passage of (14)C through the whole TCA cycle) and activities of pyruvate dehydrogenase, citrate synthase, alpha-ketoglutarate dehydrogenase, and fumarase in white structures were 10-23% of cortical values, optic nerve showing the lowest values. The data suggest a higher glycolytic than oxidative metabolism in white matter, possibly leading to surplus formation of pyruvate or lactate. Phosphoglucomutase activity, which interconverts glucose-6-phosphate and glucose-1-phosphate, was similar in white structures and parietal cortex ( approximately 3 nmol/mg tissue/min), in spite of the lower glucose uptake in the former, suggesting that a larger fraction of glucose is converted into glucose-1-phosphate in white than in gray matter. However, the white matter glycogen synthase level was only 20-40% of that in cortex, suggesting that not all glucose-1-phosphate is destined for glycogen formation.