The urea cycle of rat white adipose tissue

Arriarán, Sofía; Agnelli, Silvia; Remesar, Xavier; Fernández-López, José Antonio

doi:10.1039/c5ra16398f

Cited by 13 publications

(22 citation statements)

References 56 publications

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“…In previous works, we have proven the remarkable metabolic activity of the sum of WAT depots (i.e., taken as adipose organ) (Arriarán et al, 2015b; Arriarán et al, 2015c), especially its considerable glycolytic capability (under normoxic conditions) (Arriarán et al, 2015c; Romero et al, 2015), which adds to its known ability to store fatty acids taken from plasma lipoproteins (Garfinkel, Baker & Schotz, 1967; Wang et al, 2016) or synthesized from glucose (Guerre-Millo, 2003). Its important contribution to amino acid metabolism (Arriarán et al, 2015a), second only to liver (Agnelli et al, 2016; Arriarán et al, 2016), supports the long-proposed active WAT implication in energy and intermediate/substrate metabolism (Cahill, 1962). The data presented here only compound the puzzle, since the actual mass of cells doing the work is only a small fraction of the tissue, much lower than usually assumed.…”

Section: Discussionsupporting

confidence: 62%

“…In any case, its main acknowledged role is to contribute to the defense of energy homoeostasis, helping to control glucose (Sabater et al, 2014), lipid (Deschênes et al, 2003; Wang et al, 2016), and amino acid (Arriarán et al, 2015a) metabolism overall. It is responsible for an important share of the control of whole body energy availability (Hall, Roberts & Vora, 2009; Choe et al, 2016), and acts as a platform for the immune system, being actively implicated in processes of protection and repair (Parker & Katz, 2006; Dixit, 2008).…”

Section: Introductionmentioning

confidence: 99%

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Quantitative analysis of rat adipose tissue cell recovery, and non-fat cell volume, in primary cell cultures

Rotondo

Romero

Ho-Palma

et al. 2016

PeerJ

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BackgroundWhite adipose tissue (WAT) is a complex, diffuse, multifunctional organ which contains adipocytes, and a large proportion of fat, but also other cell types, active in defense, regeneration and signalling functions. Studies with adipocytes often require their isolation from WAT by breaking up the matrix of collagen fibres; however, it is unclear to what extent adipocyte number in primary cultures correlates with their number in intact WAT, since recovery and viability are often unknown.Experimental DesignEpididymal WAT of four young adult rats was used to isolate adipocytes with collagenase. Careful recording of lipid content of tissue, and all fraction volumes and weights, allowed us to trace the amount of initial WAT fat remaining in the cell preparation. Functionality was estimated by incubation with glucose and measurement of glucose uptake and lactate, glycerol and NEFA excretion rates up to 48 h. Non-adipocyte cells were also recovered and their sizes (and those of adipocytes) were measured. The presence of non-nucleated cells (erythrocytes) was also estimated.ResultsCell numbers and sizes were correlated from all fractions to intact WAT. Tracing the lipid content, the recovery of adipocytes in the final, metabolically active, preparation was in the range of 70–75%. Cells showed even higher metabolic activity in the second than in the first day of incubation. Adipocytes were 7%, erythrocytes 66% and other stromal (nucleated cells) 27% of total WAT cells. However, their overall volumes were 90%, 0.05%, and 0.2% of WAT. Non-fat volume of adipocytes was 1.3% of WAT.ConclusionsThe methodology presented here allows for a direct quantitative reference to the original tissue of studies using isolated cells. We have also found that the “live cell mass” of adipose tissue is very small: about 13 µL/g for adipocytes and 2 µL/g stromal, plus about 1 µL/g blood (the rats were killed by exsanguination). These data translate (with respect to the actual “live cytoplasm” size) into an extremely high metabolic activity, which make WAT an even more significant agent in the control of energy metabolism.

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Section: Discussionsupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Quantitative analysis of rat adipose tissue cell recovery, and non-fat cell volume, in primary cell cultures

Rotondo

Romero

Ho-Palma

et al. 2016

PeerJ

Self Cite

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“…We have found, recently, that adipocytes glycolyze huge amounts of glucose to lactate and glycerol 28 , acting, essentially, as an anaerobic tissue under normoxic conditions, such as those used in the present study, and this mechanism extends to the in vivo conditions 29 . We have also found that WAT contains a full urea cycle 58 and a potentially active amino acid metabolism 14 . The results obtained, and a growing list of unique capabilities of WAT [59][60][61][62][63][64] has decided us to focus on the quantitative analysis of WAT metabolism.…”

Section: Discussionmentioning

confidence: 92%

A method for the measurement of lactate, glycerol and fatty acid production from¹⁴C-glucose in primary cultures of rat epididymal adipocytes

et al. 2016

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We developed a method for the analysis of the main metabolic products of utilization of glucose by isolated adipocytes. They were incubated 24 h with 14 C-glucose. The final label distribution and cold levels of medium glucose, lactate and glycerol were estimated. Medium lactate was extracted using ion-exchange resin minicolumns prepared with centrifugation-filtering tubes in which the filter was substituted by the resin. This allowed complete washings using only 0.2 mL. Repeated washings allowed for complete recovery of fractions with low volumes passing through or retained (and eluted), which allowed precise counting and sufficient sample for further analyses. Lactate was separated from glucose and glycerol; glucose was then separated by oxidizing it to gluconate with glucose oxidase, and glycerol was separated in parallel by phosphorylation with ATP and glycerol kinase. Cells' lipid was extracted with ether and saponified. Glycerides-glycerol and fatty acids (from the soaps) were counted separately. The complete analysis of cells incubated with labelled glucose resulted in about half of the glucose metabolized in 24 h, 2/3rds of the incorporated glucose label was found as lactate, 14 % as free glycerol. Their specific activities per carbon were the same as that of glucose. Production of fatty acids took about 5 % of the label incorporated, a similar amount to that of glyceridesglycerol and estimated carbon dioxide. The procedure described is versatile enough to be used under experimental conditions, with a high degree or repeatability and with only about 3 % of the label not accounted for.

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“…However, both intestine and kidney have functional (albeit complementary) urea cycles 26,27 . We have found, recently, a robust presence of urea cycle in white adipose tissue 28 , which is unaffected by sex and anatomical site 29 _ENREF_28.…”

Section: Introductionmentioning

confidence: 78%

“…Enzyme activities were expressed per unit of protein weight. The methods used were largely based in our parallel development of methods for analysis on white adipose tissue, extensively described in a previous publication 28 .…”

Section: Enzyme Activity Analysesmentioning

confidence: 99%

Modulation of rat liver urea cycle and related ammonium metabolism by sex and cafeteria diet

et al. 2016

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High-energy (hyperlipidic) cafeteria diets induce insulin resistance limiting glucose oxidation, and lower amino acid catabolism. Despite high amino-N intake, amino acids are preserved, lowering urea excretion. We analysed how energy partition induced by cafeteria diet affects liver ammonium handling and urea cycle. Female and male rats were fed control or cafeteria diets for 30 days. There was a remarkable constancy on enzyme activities and expressions of urea cycle and ammonium metabolism. The key enzymes controlling urea cycle: carbamoyl-P synthase 1, arginino-succinate synthase and arginase expressions were decreased by diet (albeit more markedly in males), and their activities were correlated with the gene expressions. The effects observed, in ammonium handling enzyme activities and expressions behaved in a way similar to that of the urea cycle, showing a generalized downregulation of liver amino acid catabolism. This process was affected by sex. The different strategies of amino-N handling by females and males further modulated the preservation of 2-amino N under sufficient available energy. The effects of sex were more marked than those of diet were, since different metabolism survival strategies changed substrate partition and fate. The data presented suggest a lower than expected N flow to the liver, which overall importance for amino acid metabolism tends to decrease with both cafeteria diet and female sex.Under standard conditions, liver availability of ammonium was low and controlled. The situation was unchanged (or even lowered) in cafeteria-fed rats, ultimately depending on intestinal amino acid catabolism

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The urea cycle of rat white adipose tissue

Abstract: White adipose tissue urea-cycle enzymes showed a high activity and gene expression, second only to liver in catalytic capacity.

Cited by 13 publications

References 56 publications

Quantitative analysis of rat adipose tissue cell recovery, and non-fat cell volume, in primary cell cultures

Quantitative analysis of rat adipose tissue cell recovery, and non-fat cell volume, in primary cell cultures

A method for the measurement of lactate, glycerol and fatty acid production from¹⁴C-glucose in primary cultures of rat epididymal adipocytes

Modulation of rat liver urea cycle and related ammonium metabolism by sex and cafeteria diet

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The urea cycle of rat white adipose tissue

Abstract: White adipose tissue urea-cycle enzymes showed a high activity and gene expression, second only to liver in catalytic capacity.

Cited by 13 publications

References 56 publications

Quantitative analysis of rat adipose tissue cell recovery, and non-fat cell volume, in primary cell cultures

Quantitative analysis of rat adipose tissue cell recovery, and non-fat cell volume, in primary cell cultures

A method for the measurement of lactate, glycerol and fatty acid production from14C-glucose in primary cultures of rat epididymal adipocytes

Modulation of rat liver urea cycle and related ammonium metabolism by sex and cafeteria diet

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A method for the measurement of lactate, glycerol and fatty acid production from¹⁴C-glucose in primary cultures of rat epididymal adipocytes