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Metabolic fate of fructose in human adipocytes: a targeted (13)C tracer fate association study.

Varma V, Boros LG, Nolen GT, Chang CW, Wabitsch M, Beger RD, Kaput J - Metabolomics (2014)

Bottom Line: A targeted stable isotope tracer fate association method was used to analyze metabolic fluxes and flux surrogates with exposure to escalating fructose concentration.This study demonstrated that fructose stimulates anabolic processes in adipocytes robustly, including glutamate and de novo fatty acid synthesis.Furthermore, fructose also augments the release of free palmitate from fully differentiated adipocytes.

View Article: PubMed Central - PubMed

Affiliation: Division of Systems Biology, National Center for Toxicological Research, FDA, 3900 NCTR Road, Jefferson, AR 72079 USA.

ABSTRACT

The development of obesity is becoming an international problem and the role of fructose is unclear. Studies using liver tissue and hepatocytes have contributed to the understanding of fructose metabolism. Excess fructose consumption also affects extra hepatic tissues including adipose tissue. The effects of fructose on human adipocytes are not yet fully characterized, although in vivo studies have noted increased adiposity and weight gain in response to fructose sweetened-beverages. In order to understand and predict the metabolic responses of adipocytes to fructose, this study examined differentiating and differentiated human adipocytes in culture, exposed to a range of fructose concentrations equivalent to that reported in blood after consuming fructose. A stable isotope based dynamic profiling method using [U-(13)C6]-d-fructose tracer was used to examine the metabolism and fate of fructose. A targeted stable isotope tracer fate association method was used to analyze metabolic fluxes and flux surrogates with exposure to escalating fructose concentration. This study demonstrated that fructose stimulates anabolic processes in adipocytes robustly, including glutamate and de novo fatty acid synthesis. Furthermore, fructose also augments the release of free palmitate from fully differentiated adipocytes. These results imply that in the presence of fructose, the metabolic response of adipocytes in culture is altered in a dose dependent manner, particularly favoring increased glutamate and fatty acid synthesis and release, warranting further in vivo studies.

No MeSH data available.


Related in: MedlinePlus

Fructose-induced synthesis and release of palmitate (C16:0) in adipocytes. Adipocytes were exposed to 0.1, 0.5, 1, 2.5, 5, 7.5 or 10 mM fructose in a medium containing a baseline amount of 5 mM glucose from the initiation of differentiation for 8 days (differentiating adipocytes) or 16 days (differentiated adipocytes). 10 % of fructose was supplied as [U-13C6]-fructose for a period of 48 h before harvest. 13C content (Σmn) of intracellular palmitate in differentiating (a) and differentiated (b) adipocytes. 13C labeled newly synthesized intracellular palmitate in differentiating (c) and differentiated (d) adipocytes, 13C content (Σmn) of extracellular palmitate in the medium form differentiating (e) and differentiated (f) adipocytes
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Fig4: Fructose-induced synthesis and release of palmitate (C16:0) in adipocytes. Adipocytes were exposed to 0.1, 0.5, 1, 2.5, 5, 7.5 or 10 mM fructose in a medium containing a baseline amount of 5 mM glucose from the initiation of differentiation for 8 days (differentiating adipocytes) or 16 days (differentiated adipocytes). 10 % of fructose was supplied as [U-13C6]-fructose for a period of 48 h before harvest. 13C content (Σmn) of intracellular palmitate in differentiating (a) and differentiated (b) adipocytes. 13C labeled newly synthesized intracellular palmitate in differentiating (c) and differentiated (d) adipocytes, 13C content (Σmn) of extracellular palmitate in the medium form differentiating (e) and differentiated (f) adipocytes

Mentions: Fructose-derived pyruvate enters the TCA cycle via the PDH flux or PC flux. Entry through the PDH flux results in the formation of acetyl-CoA that combines with oxaloacetate to form citrate. When excess citrate is formed, it can be shuttled out of the mitochondria and metabolized to form acetyl-CoA. In combination with malonyl-CoA, acetyl-CoA acts as a substrate for anabolic reactions of the lipogenesis pathway leading to the synthesis of fatty acids such as palmitate (C16:0). We found a statistically significant increase in intracellular [13C]-palmitate formed in differentiating (Fig. 4a) and differentiated adipocytes (Fig. 4b) exposed to increased levels of fructose. The increase in labeled palmitate was more pronounced in the differentiated adipocytes (Fig. 4b). These results demonstrated that fructose was robustly converted to palmitate in adipocytes and was therefore a potent lipogenic substrate in this cell type. The result was consistent with increasing mobilization of fructose towards fatty acid synthesis. Newly synthesized palmitate contributed only about 5 % of the total fatty acids at 0.1 mM fructose in both the differentiating (Fig. 4c) and fully differentiated adipocytes (Fig. 4d). A dose dependent increase in the newly synthesized palmitate occurred in adipocytes cultured in the presence of 5 mM or higher fructose (Fig. 4c, d). This response was more robust in differentiated adipocytes (Fig. 4d) which exhibited a two to ninefold increase in newly synthesized palmitate between 2.5 and 10 mM, supporting the conclusion that high concentrations of fructose increased lipogenesis.Fig. 4


Metabolic fate of fructose in human adipocytes: a targeted (13)C tracer fate association study.

Varma V, Boros LG, Nolen GT, Chang CW, Wabitsch M, Beger RD, Kaput J - Metabolomics (2014)

Fructose-induced synthesis and release of palmitate (C16:0) in adipocytes. Adipocytes were exposed to 0.1, 0.5, 1, 2.5, 5, 7.5 or 10 mM fructose in a medium containing a baseline amount of 5 mM glucose from the initiation of differentiation for 8 days (differentiating adipocytes) or 16 days (differentiated adipocytes). 10 % of fructose was supplied as [U-13C6]-fructose for a period of 48 h before harvest. 13C content (Σmn) of intracellular palmitate in differentiating (a) and differentiated (b) adipocytes. 13C labeled newly synthesized intracellular palmitate in differentiating (c) and differentiated (d) adipocytes, 13C content (Σmn) of extracellular palmitate in the medium form differentiating (e) and differentiated (f) adipocytes
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig4: Fructose-induced synthesis and release of palmitate (C16:0) in adipocytes. Adipocytes were exposed to 0.1, 0.5, 1, 2.5, 5, 7.5 or 10 mM fructose in a medium containing a baseline amount of 5 mM glucose from the initiation of differentiation for 8 days (differentiating adipocytes) or 16 days (differentiated adipocytes). 10 % of fructose was supplied as [U-13C6]-fructose for a period of 48 h before harvest. 13C content (Σmn) of intracellular palmitate in differentiating (a) and differentiated (b) adipocytes. 13C labeled newly synthesized intracellular palmitate in differentiating (c) and differentiated (d) adipocytes, 13C content (Σmn) of extracellular palmitate in the medium form differentiating (e) and differentiated (f) adipocytes
Mentions: Fructose-derived pyruvate enters the TCA cycle via the PDH flux or PC flux. Entry through the PDH flux results in the formation of acetyl-CoA that combines with oxaloacetate to form citrate. When excess citrate is formed, it can be shuttled out of the mitochondria and metabolized to form acetyl-CoA. In combination with malonyl-CoA, acetyl-CoA acts as a substrate for anabolic reactions of the lipogenesis pathway leading to the synthesis of fatty acids such as palmitate (C16:0). We found a statistically significant increase in intracellular [13C]-palmitate formed in differentiating (Fig. 4a) and differentiated adipocytes (Fig. 4b) exposed to increased levels of fructose. The increase in labeled palmitate was more pronounced in the differentiated adipocytes (Fig. 4b). These results demonstrated that fructose was robustly converted to palmitate in adipocytes and was therefore a potent lipogenic substrate in this cell type. The result was consistent with increasing mobilization of fructose towards fatty acid synthesis. Newly synthesized palmitate contributed only about 5 % of the total fatty acids at 0.1 mM fructose in both the differentiating (Fig. 4c) and fully differentiated adipocytes (Fig. 4d). A dose dependent increase in the newly synthesized palmitate occurred in adipocytes cultured in the presence of 5 mM or higher fructose (Fig. 4c, d). This response was more robust in differentiated adipocytes (Fig. 4d) which exhibited a two to ninefold increase in newly synthesized palmitate between 2.5 and 10 mM, supporting the conclusion that high concentrations of fructose increased lipogenesis.Fig. 4

Bottom Line: A targeted stable isotope tracer fate association method was used to analyze metabolic fluxes and flux surrogates with exposure to escalating fructose concentration.This study demonstrated that fructose stimulates anabolic processes in adipocytes robustly, including glutamate and de novo fatty acid synthesis.Furthermore, fructose also augments the release of free palmitate from fully differentiated adipocytes.

View Article: PubMed Central - PubMed

Affiliation: Division of Systems Biology, National Center for Toxicological Research, FDA, 3900 NCTR Road, Jefferson, AR 72079 USA.

ABSTRACT

The development of obesity is becoming an international problem and the role of fructose is unclear. Studies using liver tissue and hepatocytes have contributed to the understanding of fructose metabolism. Excess fructose consumption also affects extra hepatic tissues including adipose tissue. The effects of fructose on human adipocytes are not yet fully characterized, although in vivo studies have noted increased adiposity and weight gain in response to fructose sweetened-beverages. In order to understand and predict the metabolic responses of adipocytes to fructose, this study examined differentiating and differentiated human adipocytes in culture, exposed to a range of fructose concentrations equivalent to that reported in blood after consuming fructose. A stable isotope based dynamic profiling method using [U-(13)C6]-d-fructose tracer was used to examine the metabolism and fate of fructose. A targeted stable isotope tracer fate association method was used to analyze metabolic fluxes and flux surrogates with exposure to escalating fructose concentration. This study demonstrated that fructose stimulates anabolic processes in adipocytes robustly, including glutamate and de novo fatty acid synthesis. Furthermore, fructose also augments the release of free palmitate from fully differentiated adipocytes. These results imply that in the presence of fructose, the metabolic response of adipocytes in culture is altered in a dose dependent manner, particularly favoring increased glutamate and fatty acid synthesis and release, warranting further in vivo studies.

No MeSH data available.


Related in: MedlinePlus