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Glycerol Production from Glucose and Fructose by 3T3-L1 Cells: A Mechanism of Adipocyte Defense from Excess Substrate.

Romero Mdel M, Sabater D, Fernández-López JA, Remesar X, Alemany M - PLoS ONE (2015)

Bottom Line: Fructose conversion to lactate and glycerol was lower than that of glucose.When both hexoses were present, the effects of fructose on gene expression prevailed over those of glucose.A phosphatase pathway such as that described may have a potential regulatory function, and explain the production of glycerol by adipocytes in the absence of lipolytic stimulation.

View Article: PubMed Central - PubMed

Affiliation: Department of Nutrition and Food Science, Faculty of Biology, University of Barcelona, Av.Diagonal 643, 08028, Barcelona, Spain; Institute of Biomedicine, University of Barcelona, Barcelona, Spain; CIBER Obesity and Nutrition, Barcelona, Spain.

ABSTRACT
Cultured adipocytes (3T3-L1) produce large amounts of 3C fragments; largely lactate, depending on medium glucose levels. Increased glycolysis has been observed also in vivo in different sites of rat white adipose tissue. We investigated whether fructose can substitute glucose as source of lactate, and, especially whether the glycerol released to the medium was of lipolytic or glycolytic origin. Fructose conversion to lactate and glycerol was lower than that of glucose. The fast exhaustion of medium glucose was unrelated to significant changes in lipid storage. Fructose inhibited to a higher degree than glucose the expression of lipogenic enzymes. When both hexoses were present, the effects of fructose on gene expression prevailed over those of glucose. Adipocytes expressed fructokinase, but not aldolase b. Substantive release of glycerol accompanied lactate when fructose was the substrate. The mass of cell triacylglycerol (and its lack of change) could not justify the comparatively higher amount of glycerol released. Consequently, most of this glycerol should be derived from the glycolytic pathway, since its lipolytic origin could not be (quantitatively) sustained. Proportionally (with respect to lactate plus glycerol), more glycerol was produced from fructose than from glucose, which suggests that part of fructose was catabolized by the alternate (hepatic) fructose pathway. Earlier described adipose glycerophophatase activity may help explain the glycolytic origin of most of the glycerol. However, no gene is known for this enzyme in mammals, which suggests that this function may be carried out by one of the known phosphatases in the tissue. Break up of glycerol-3P to yield glycerol, may be a limiting factor for the synthesis of triacylglycerols through control of glycerol-3P availability. A phosphatase pathway such as that described may have a potential regulatory function, and explain the production of glycerol by adipocytes in the absence of lipolytic stimulation.

No MeSH data available.


Related in: MedlinePlus

Gene expression of enzymes of glucose/ fructose metabolism and triacylglycerol synthesis in 3T3-L1 adipocytes exposed to a medium with varying concentrations of glucose, fructose or a combination of both.Solid lines represent the paths analyzed in this Fig and in Fig 4; blue triangles indicate the sites of production and utilization of NADH. The graphs indicate the number of copies of specific mRNAs for the genes (in black) corresponding to the enzymes and transporters (in green) acting on the corresponding paths (linked by red dotted lines). In each graph, the expressions in the presence of glucose are marked in blue, and those with fructose in red. The mixed-hexose groups are marked in purple. Each point corresponds to the mean ± sem of three different wells. Abbreviations: glc = glucose; frc = fructose; dha-P = dihydroxyacetone-P; glyc = glycerol; glyc-ald = glyceraldehyde; glyc-acid = glycerate; lact = lactate; pyr = pyruvate; TAG = triacylglycerols; acetCoA = acetyl-CoA; FA = fatty acids. The statistical significance of the differences between groups presented here correspond to Figs 3 and 4. The effect of hexose was analyzed with two-way anova: glucose or fructose vs. concentration (in this case, for the sake of clarity, the mixed hexose groups were not included in the analysis). The differences between glc and frc groups were significant (p<0.0001) for all genes except Hk2 (P = 0.0190), and Aldoa (0.0011) and not significant only for Adh4. The effect of "concentration" was analyzed using one-way anova analyses for glucose, fructose and their mixture. For glucose, all genes responses were significant (P values between 0.05 and 0.0001) except Glut4, Ldha, Acc1, Pdk4, Aldh2, Lpl, Acp5 and Aqp7 (NS). Changes of gene expression with fructose concentration were all statistically significant except for Hk1, Pfkm, Acc1, and Gpam (NS). In the case of glc+frc, all genes responded significantly to hexose concentration except Glut4, Pfkm, Ldhb, Acc1, Fas, Gpam, Pdk4, Aldh1a1, Atgl, Hsl, and Acp2
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pone.0139502.g004: Gene expression of enzymes of glucose/ fructose metabolism and triacylglycerol synthesis in 3T3-L1 adipocytes exposed to a medium with varying concentrations of glucose, fructose or a combination of both.Solid lines represent the paths analyzed in this Fig and in Fig 4; blue triangles indicate the sites of production and utilization of NADH. The graphs indicate the number of copies of specific mRNAs for the genes (in black) corresponding to the enzymes and transporters (in green) acting on the corresponding paths (linked by red dotted lines). In each graph, the expressions in the presence of glucose are marked in blue, and those with fructose in red. The mixed-hexose groups are marked in purple. Each point corresponds to the mean ± sem of three different wells. Abbreviations: glc = glucose; frc = fructose; dha-P = dihydroxyacetone-P; glyc = glycerol; glyc-ald = glyceraldehyde; glyc-acid = glycerate; lact = lactate; pyr = pyruvate; TAG = triacylglycerols; acetCoA = acetyl-CoA; FA = fatty acids. The statistical significance of the differences between groups presented here correspond to Figs 3 and 4. The effect of hexose was analyzed with two-way anova: glucose or fructose vs. concentration (in this case, for the sake of clarity, the mixed hexose groups were not included in the analysis). The differences between glc and frc groups were significant (p<0.0001) for all genes except Hk2 (P = 0.0190), and Aldoa (0.0011) and not significant only for Adh4. The effect of "concentration" was analyzed using one-way anova analyses for glucose, fructose and their mixture. For glucose, all genes responses were significant (P values between 0.05 and 0.0001) except Glut4, Ldha, Acc1, Pdk4, Aldh2, Lpl, Acp5 and Aqp7 (NS). Changes of gene expression with fructose concentration were all statistically significant except for Hk1, Pfkm, Acc1, and Gpam (NS). In the case of glc+frc, all genes responded significantly to hexose concentration except Glut4, Pfkm, Ldhb, Acc1, Fas, Gpam, Pdk4, Aldh1a1, Atgl, Hsl, and Acp2

Mentions: Fig 4 presents a composite scheme of the changes in the expression of selected genes of glucose oxidation and lipid metabolism in 3T3-L1 cells subjected to different concentrations of glucose and fructose in the medium. Glut5 (glucose transporter 5) expression was not detected, and thus not included in the graph. The expression of Glut1 was higher than that of Glut4, and their patterns were different. Glut1 expression was higher with fructose than with glucose, and in both cases, the expression decreased with growing medium monosaccharide. Glut4 reversed this pattern; showing higher (and maintained with increasing glucose levels) expressions for glucose. Fructose decreased its expression markedly with little change in function of hexose concentration. Both hexokinases gene (Hk1 and Hk2) expressions tended to decrease with increasing hexose concentrations, with significant differences between fructose and glucose for Hk1, but not for Hk2. We found a robust basal expression of the fructokinase gene (Khk), inhibited by fructose; its expression also decreased with increasing concentrations of glucose.


Glycerol Production from Glucose and Fructose by 3T3-L1 Cells: A Mechanism of Adipocyte Defense from Excess Substrate.

Romero Mdel M, Sabater D, Fernández-López JA, Remesar X, Alemany M - PLoS ONE (2015)

Gene expression of enzymes of glucose/ fructose metabolism and triacylglycerol synthesis in 3T3-L1 adipocytes exposed to a medium with varying concentrations of glucose, fructose or a combination of both.Solid lines represent the paths analyzed in this Fig and in Fig 4; blue triangles indicate the sites of production and utilization of NADH. The graphs indicate the number of copies of specific mRNAs for the genes (in black) corresponding to the enzymes and transporters (in green) acting on the corresponding paths (linked by red dotted lines). In each graph, the expressions in the presence of glucose are marked in blue, and those with fructose in red. The mixed-hexose groups are marked in purple. Each point corresponds to the mean ± sem of three different wells. Abbreviations: glc = glucose; frc = fructose; dha-P = dihydroxyacetone-P; glyc = glycerol; glyc-ald = glyceraldehyde; glyc-acid = glycerate; lact = lactate; pyr = pyruvate; TAG = triacylglycerols; acetCoA = acetyl-CoA; FA = fatty acids. The statistical significance of the differences between groups presented here correspond to Figs 3 and 4. The effect of hexose was analyzed with two-way anova: glucose or fructose vs. concentration (in this case, for the sake of clarity, the mixed hexose groups were not included in the analysis). The differences between glc and frc groups were significant (p<0.0001) for all genes except Hk2 (P = 0.0190), and Aldoa (0.0011) and not significant only for Adh4. The effect of "concentration" was analyzed using one-way anova analyses for glucose, fructose and their mixture. For glucose, all genes responses were significant (P values between 0.05 and 0.0001) except Glut4, Ldha, Acc1, Pdk4, Aldh2, Lpl, Acp5 and Aqp7 (NS). Changes of gene expression with fructose concentration were all statistically significant except for Hk1, Pfkm, Acc1, and Gpam (NS). In the case of glc+frc, all genes responded significantly to hexose concentration except Glut4, Pfkm, Ldhb, Acc1, Fas, Gpam, Pdk4, Aldh1a1, Atgl, Hsl, and Acp2
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Related In: Results  -  Collection

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pone.0139502.g004: Gene expression of enzymes of glucose/ fructose metabolism and triacylglycerol synthesis in 3T3-L1 adipocytes exposed to a medium with varying concentrations of glucose, fructose or a combination of both.Solid lines represent the paths analyzed in this Fig and in Fig 4; blue triangles indicate the sites of production and utilization of NADH. The graphs indicate the number of copies of specific mRNAs for the genes (in black) corresponding to the enzymes and transporters (in green) acting on the corresponding paths (linked by red dotted lines). In each graph, the expressions in the presence of glucose are marked in blue, and those with fructose in red. The mixed-hexose groups are marked in purple. Each point corresponds to the mean ± sem of three different wells. Abbreviations: glc = glucose; frc = fructose; dha-P = dihydroxyacetone-P; glyc = glycerol; glyc-ald = glyceraldehyde; glyc-acid = glycerate; lact = lactate; pyr = pyruvate; TAG = triacylglycerols; acetCoA = acetyl-CoA; FA = fatty acids. The statistical significance of the differences between groups presented here correspond to Figs 3 and 4. The effect of hexose was analyzed with two-way anova: glucose or fructose vs. concentration (in this case, for the sake of clarity, the mixed hexose groups were not included in the analysis). The differences between glc and frc groups were significant (p<0.0001) for all genes except Hk2 (P = 0.0190), and Aldoa (0.0011) and not significant only for Adh4. The effect of "concentration" was analyzed using one-way anova analyses for glucose, fructose and their mixture. For glucose, all genes responses were significant (P values between 0.05 and 0.0001) except Glut4, Ldha, Acc1, Pdk4, Aldh2, Lpl, Acp5 and Aqp7 (NS). Changes of gene expression with fructose concentration were all statistically significant except for Hk1, Pfkm, Acc1, and Gpam (NS). In the case of glc+frc, all genes responded significantly to hexose concentration except Glut4, Pfkm, Ldhb, Acc1, Fas, Gpam, Pdk4, Aldh1a1, Atgl, Hsl, and Acp2
Mentions: Fig 4 presents a composite scheme of the changes in the expression of selected genes of glucose oxidation and lipid metabolism in 3T3-L1 cells subjected to different concentrations of glucose and fructose in the medium. Glut5 (glucose transporter 5) expression was not detected, and thus not included in the graph. The expression of Glut1 was higher than that of Glut4, and their patterns were different. Glut1 expression was higher with fructose than with glucose, and in both cases, the expression decreased with growing medium monosaccharide. Glut4 reversed this pattern; showing higher (and maintained with increasing glucose levels) expressions for glucose. Fructose decreased its expression markedly with little change in function of hexose concentration. Both hexokinases gene (Hk1 and Hk2) expressions tended to decrease with increasing hexose concentrations, with significant differences between fructose and glucose for Hk1, but not for Hk2. We found a robust basal expression of the fructokinase gene (Khk), inhibited by fructose; its expression also decreased with increasing concentrations of glucose.

Bottom Line: Fructose conversion to lactate and glycerol was lower than that of glucose.When both hexoses were present, the effects of fructose on gene expression prevailed over those of glucose.A phosphatase pathway such as that described may have a potential regulatory function, and explain the production of glycerol by adipocytes in the absence of lipolytic stimulation.

View Article: PubMed Central - PubMed

Affiliation: Department of Nutrition and Food Science, Faculty of Biology, University of Barcelona, Av.Diagonal 643, 08028, Barcelona, Spain; Institute of Biomedicine, University of Barcelona, Barcelona, Spain; CIBER Obesity and Nutrition, Barcelona, Spain.

ABSTRACT
Cultured adipocytes (3T3-L1) produce large amounts of 3C fragments; largely lactate, depending on medium glucose levels. Increased glycolysis has been observed also in vivo in different sites of rat white adipose tissue. We investigated whether fructose can substitute glucose as source of lactate, and, especially whether the glycerol released to the medium was of lipolytic or glycolytic origin. Fructose conversion to lactate and glycerol was lower than that of glucose. The fast exhaustion of medium glucose was unrelated to significant changes in lipid storage. Fructose inhibited to a higher degree than glucose the expression of lipogenic enzymes. When both hexoses were present, the effects of fructose on gene expression prevailed over those of glucose. Adipocytes expressed fructokinase, but not aldolase b. Substantive release of glycerol accompanied lactate when fructose was the substrate. The mass of cell triacylglycerol (and its lack of change) could not justify the comparatively higher amount of glycerol released. Consequently, most of this glycerol should be derived from the glycolytic pathway, since its lipolytic origin could not be (quantitatively) sustained. Proportionally (with respect to lactate plus glycerol), more glycerol was produced from fructose than from glucose, which suggests that part of fructose was catabolized by the alternate (hepatic) fructose pathway. Earlier described adipose glycerophophatase activity may help explain the glycolytic origin of most of the glycerol. However, no gene is known for this enzyme in mammals, which suggests that this function may be carried out by one of the known phosphatases in the tissue. Break up of glycerol-3P to yield glycerol, may be a limiting factor for the synthesis of triacylglycerols through control of glycerol-3P availability. A phosphatase pathway such as that described may have a potential regulatory function, and explain the production of glycerol by adipocytes in the absence of lipolytic stimulation.

No MeSH data available.


Related in: MedlinePlus