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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

Glucose and fructose consumption by 3T3-L1 adipocytes exposed to a medium with varying concentrations of glucose, fructose or a combination of both.Each dot represents the mean ± sem of three different wells. Glucose or hexose consumption are expressed in pmol per cell and day. There were statistically significant (two-way anova) differences (P<0.05) for 11 mM and 22 mM glucose absorption data on day 1 vs. days 2 and 3 (the latter only for 22 mM glucose). There were significant differences for fructose vs. glucose consumption for concentrations higher than 5.5 mM and for days 1 to 3. Fructose consumption in the presence of glucose was also statistically different from that of glucose in the presence of fructose for 2.75 mM to 5.5 mM initial medium levels. In the graphs where glucose + fructose were present in the medium, the X-axis legend shows the hexose measured, and the other present but not shown in the graph is represented between brackets.
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pone.0139502.g002: Glucose and fructose consumption by 3T3-L1 adipocytes exposed to a medium with varying concentrations of glucose, fructose or a combination of both.Each dot represents the mean ± sem of three different wells. Glucose or hexose consumption are expressed in pmol per cell and day. There were statistically significant (two-way anova) differences (P<0.05) for 11 mM and 22 mM glucose absorption data on day 1 vs. days 2 and 3 (the latter only for 22 mM glucose). There were significant differences for fructose vs. glucose consumption for concentrations higher than 5.5 mM and for days 1 to 3. Fructose consumption in the presence of glucose was also statistically different from that of glucose in the presence of fructose for 2.75 mM to 5.5 mM initial medium levels. In the graphs where glucose + fructose were present in the medium, the X-axis legend shows the hexose measured, and the other present but not shown in the graph is represented between brackets.

Mentions: Since the final counts of cells per well were variable, the data on glucose or fructose consumption (i.e. decrease in medium sugar levels) were corrected by the number of cells. Fig 2 shows the rates of consumption of glucose and fructose per cell and day. Glucose consumption increased in proportion to the initial glucose added up to 11 mM, stabilizing thereafter. In fact, these data correspond to a consumption higher than 77% of glucose in the medium, up to 11 mM. This Fig corresponds to the maximal capacity of the cells to use glucose as substrate through glycolysis. The presence of added fructose did not change the efficiency of glucose handling. However, there was a significant difference in the rates of glucose utilization with time: the limit of consumption was lower (in the range of 20 pmol/cell·day) on the first day; but on the second and third, the rates practically doubled. The rates of consumption of medium fructose were much lower, and tended to decrease with a prolonged exposure to fructose. The data presented suggest that the combination of glucose and fructose resulted in the practical exhaustion of glucose, with only a minimal (albeit variable) amount of fructose used.


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)

Glucose and fructose consumption by 3T3-L1 adipocytes exposed to a medium with varying concentrations of glucose, fructose or a combination of both.Each dot represents the mean ± sem of three different wells. Glucose or hexose consumption are expressed in pmol per cell and day. There were statistically significant (two-way anova) differences (P<0.05) for 11 mM and 22 mM glucose absorption data on day 1 vs. days 2 and 3 (the latter only for 22 mM glucose). There were significant differences for fructose vs. glucose consumption for concentrations higher than 5.5 mM and for days 1 to 3. Fructose consumption in the presence of glucose was also statistically different from that of glucose in the presence of fructose for 2.75 mM to 5.5 mM initial medium levels. In the graphs where glucose + fructose were present in the medium, the X-axis legend shows the hexose measured, and the other present but not shown in the graph is represented between brackets.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4591265&req=5

pone.0139502.g002: Glucose and fructose consumption by 3T3-L1 adipocytes exposed to a medium with varying concentrations of glucose, fructose or a combination of both.Each dot represents the mean ± sem of three different wells. Glucose or hexose consumption are expressed in pmol per cell and day. There were statistically significant (two-way anova) differences (P<0.05) for 11 mM and 22 mM glucose absorption data on day 1 vs. days 2 and 3 (the latter only for 22 mM glucose). There were significant differences for fructose vs. glucose consumption for concentrations higher than 5.5 mM and for days 1 to 3. Fructose consumption in the presence of glucose was also statistically different from that of glucose in the presence of fructose for 2.75 mM to 5.5 mM initial medium levels. In the graphs where glucose + fructose were present in the medium, the X-axis legend shows the hexose measured, and the other present but not shown in the graph is represented between brackets.
Mentions: Since the final counts of cells per well were variable, the data on glucose or fructose consumption (i.e. decrease in medium sugar levels) were corrected by the number of cells. Fig 2 shows the rates of consumption of glucose and fructose per cell and day. Glucose consumption increased in proportion to the initial glucose added up to 11 mM, stabilizing thereafter. In fact, these data correspond to a consumption higher than 77% of glucose in the medium, up to 11 mM. This Fig corresponds to the maximal capacity of the cells to use glucose as substrate through glycolysis. The presence of added fructose did not change the efficiency of glucose handling. However, there was a significant difference in the rates of glucose utilization with time: the limit of consumption was lower (in the range of 20 pmol/cell·day) on the first day; but on the second and third, the rates practically doubled. The rates of consumption of medium fructose were much lower, and tended to decrease with a prolonged exposure to fructose. The data presented suggest that the combination of glucose and fructose resulted in the practical exhaustion of glucose, with only a minimal (albeit variable) amount of fructose used.

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