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High fat diet induces dysregulation of hepatic oxygen gradients and mitochondrial function in vivo.

Mantena SK, Vaughn DP, Andringa KK, Eccleston HB, King AL, Abrams GA, Doeller JE, Kraus DW, Darley-Usmar VM, Bailey SM - Biochem. J. (2009)

Bottom Line: NAFLD (non-alcoholic fatty liver disease), associated with obesity and the cardiometabolic syndrome, is an important medical problem affecting up to 20% of western populations.Mitochondria from the HFD group showed increased sensitivity to NO-dependent inhibition of respiration compared with controls.These findings indicate that chronic exposure to a HFD negatively affects the bioenergetics of liver mitochondria and this probably contributes to hypoxic stress and deleterious NO-dependent modification of mitochondrial proteins.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Health Sciences, Center for Free Radical Biology, The University of Alabama at Birmingham, Birmingham, AL 35294, USA.

ABSTRACT
NAFLD (non-alcoholic fatty liver disease), associated with obesity and the cardiometabolic syndrome, is an important medical problem affecting up to 20% of western populations. Evidence indicates that mitochondrial dysfunction plays a critical role in NAFLD initiation and progression to the more serious condition of NASH (non-alcoholic steatohepatitis). Herein we hypothesize that mitochondrial defects induced by exposure to a HFD (high fat diet) contribute to a hypoxic state in liver and this is associated with increased protein modification by RNS (reactive nitrogen species). To test this concept, C57BL/6 mice were pair-fed a control diet and HFD containing 35% and 71% total calories (1 cal approximately 4.184 J) from fat respectively, for 8 or 16 weeks and liver hypoxia, mitochondrial bioenergetics, NO (nitric oxide)-dependent control of respiration, and 3-NT (3-nitrotyrosine), a marker of protein modification by RNS, were examined. Feeding a HFD for 16 weeks induced NASH-like pathology accompanied by elevated triacylglycerols, increased CYP2E1 (cytochrome P450 2E1) and iNOS (inducible nitric oxide synthase) protein, and significantly enhanced hypoxia in the pericentral region of the liver. Mitochondria from the HFD group showed increased sensitivity to NO-dependent inhibition of respiration compared with controls. In addition, accumulation of 3-NT paralleled the hypoxia gradient in vivo and 3-NT levels were increased in mitochondrial proteins. Liver mitochondria from mice fed the HFD for 16 weeks exhibited depressed state 3 respiration, uncoupled respiration, cytochrome c oxidase activity, and mitochondrial membrane potential. These findings indicate that chronic exposure to a HFD negatively affects the bioenergetics of liver mitochondria and this probably contributes to hypoxic stress and deleterious NO-dependent modification of mitochondrial proteins.

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Effect of HFD on respiratory rates, RCR and respiratory complex activities in liver mitochondriaState 3 and 4 respiration was measured and the RCR was determined using either glutamate/malate (A and B) or succinate (C and D) as oxidizable substrates in freshly isolated mitochondria. (E) Complex IV activity was measured by monitoring the rate of oxidation of fully reduced cytochrome c at 550 nm. (F) Complex I activity was assessed by measuring the rotenone-sensitive rate of oxidation of NADH initiated by coenzyme Q1. Complex I and IV activities were measured at the 16 week feeding time point. Values are expressed as the means±S.E.M. for six pairs of mice. *P<0.05, **P<0.01, compared with control.
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Figure 3: Effect of HFD on respiratory rates, RCR and respiratory complex activities in liver mitochondriaState 3 and 4 respiration was measured and the RCR was determined using either glutamate/malate (A and B) or succinate (C and D) as oxidizable substrates in freshly isolated mitochondria. (E) Complex IV activity was measured by monitoring the rate of oxidation of fully reduced cytochrome c at 550 nm. (F) Complex I activity was assessed by measuring the rotenone-sensitive rate of oxidation of NADH initiated by coenzyme Q1. Complex I and IV activities were measured at the 16 week feeding time point. Values are expressed as the means±S.E.M. for six pairs of mice. *P<0.05, **P<0.01, compared with control.

Mentions: Feeding a HFD resulted in alterations in mitochondrial function (Figure 3). While respiration was largely unaffected by feeding a HFD for 8 weeks, state 3 respiration was significantly decreased at 16 weeks with a slight increase in state 4 respiration (Figures 3A and 3C). This decrease in state 3 respiration translated into a significant decrease in the RCR (Figures 3B and 3D). Moreover, feeding a HFD for 16 weeks significantly decreased complex IV (cytochrome c oxidase) activity (Figure 3E), whereas complex I (NADH dehydrogenase) activity (Figure 3F) was unaffected by feeding a HFD. There was no difference in citrate synthase activity, a commonly used mitochondrial marker enzyme, between groups at 16 weeks (control, 0.845±0.05 and HFD, 0.804±0.027 μmol/min per mg of protein, P=0.39). No change in citrate synthase activity indicates that the higher levels of hepatic triacylglycerol in the HFD group had no effect on the overall content or purity of isolated mitochondria used for functional assays.


High fat diet induces dysregulation of hepatic oxygen gradients and mitochondrial function in vivo.

Mantena SK, Vaughn DP, Andringa KK, Eccleston HB, King AL, Abrams GA, Doeller JE, Kraus DW, Darley-Usmar VM, Bailey SM - Biochem. J. (2009)

Effect of HFD on respiratory rates, RCR and respiratory complex activities in liver mitochondriaState 3 and 4 respiration was measured and the RCR was determined using either glutamate/malate (A and B) or succinate (C and D) as oxidizable substrates in freshly isolated mitochondria. (E) Complex IV activity was measured by monitoring the rate of oxidation of fully reduced cytochrome c at 550 nm. (F) Complex I activity was assessed by measuring the rotenone-sensitive rate of oxidation of NADH initiated by coenzyme Q1. Complex I and IV activities were measured at the 16 week feeding time point. Values are expressed as the means±S.E.M. for six pairs of mice. *P<0.05, **P<0.01, compared with control.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2637578&req=5

Figure 3: Effect of HFD on respiratory rates, RCR and respiratory complex activities in liver mitochondriaState 3 and 4 respiration was measured and the RCR was determined using either glutamate/malate (A and B) or succinate (C and D) as oxidizable substrates in freshly isolated mitochondria. (E) Complex IV activity was measured by monitoring the rate of oxidation of fully reduced cytochrome c at 550 nm. (F) Complex I activity was assessed by measuring the rotenone-sensitive rate of oxidation of NADH initiated by coenzyme Q1. Complex I and IV activities were measured at the 16 week feeding time point. Values are expressed as the means±S.E.M. for six pairs of mice. *P<0.05, **P<0.01, compared with control.
Mentions: Feeding a HFD resulted in alterations in mitochondrial function (Figure 3). While respiration was largely unaffected by feeding a HFD for 8 weeks, state 3 respiration was significantly decreased at 16 weeks with a slight increase in state 4 respiration (Figures 3A and 3C). This decrease in state 3 respiration translated into a significant decrease in the RCR (Figures 3B and 3D). Moreover, feeding a HFD for 16 weeks significantly decreased complex IV (cytochrome c oxidase) activity (Figure 3E), whereas complex I (NADH dehydrogenase) activity (Figure 3F) was unaffected by feeding a HFD. There was no difference in citrate synthase activity, a commonly used mitochondrial marker enzyme, between groups at 16 weeks (control, 0.845±0.05 and HFD, 0.804±0.027 μmol/min per mg of protein, P=0.39). No change in citrate synthase activity indicates that the higher levels of hepatic triacylglycerol in the HFD group had no effect on the overall content or purity of isolated mitochondria used for functional assays.

Bottom Line: NAFLD (non-alcoholic fatty liver disease), associated with obesity and the cardiometabolic syndrome, is an important medical problem affecting up to 20% of western populations.Mitochondria from the HFD group showed increased sensitivity to NO-dependent inhibition of respiration compared with controls.These findings indicate that chronic exposure to a HFD negatively affects the bioenergetics of liver mitochondria and this probably contributes to hypoxic stress and deleterious NO-dependent modification of mitochondrial proteins.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Health Sciences, Center for Free Radical Biology, The University of Alabama at Birmingham, Birmingham, AL 35294, USA.

ABSTRACT
NAFLD (non-alcoholic fatty liver disease), associated with obesity and the cardiometabolic syndrome, is an important medical problem affecting up to 20% of western populations. Evidence indicates that mitochondrial dysfunction plays a critical role in NAFLD initiation and progression to the more serious condition of NASH (non-alcoholic steatohepatitis). Herein we hypothesize that mitochondrial defects induced by exposure to a HFD (high fat diet) contribute to a hypoxic state in liver and this is associated with increased protein modification by RNS (reactive nitrogen species). To test this concept, C57BL/6 mice were pair-fed a control diet and HFD containing 35% and 71% total calories (1 cal approximately 4.184 J) from fat respectively, for 8 or 16 weeks and liver hypoxia, mitochondrial bioenergetics, NO (nitric oxide)-dependent control of respiration, and 3-NT (3-nitrotyrosine), a marker of protein modification by RNS, were examined. Feeding a HFD for 16 weeks induced NASH-like pathology accompanied by elevated triacylglycerols, increased CYP2E1 (cytochrome P450 2E1) and iNOS (inducible nitric oxide synthase) protein, and significantly enhanced hypoxia in the pericentral region of the liver. Mitochondria from the HFD group showed increased sensitivity to NO-dependent inhibition of respiration compared with controls. In addition, accumulation of 3-NT paralleled the hypoxia gradient in vivo and 3-NT levels were increased in mitochondrial proteins. Liver mitochondria from mice fed the HFD for 16 weeks exhibited depressed state 3 respiration, uncoupled respiration, cytochrome c oxidase activity, and mitochondrial membrane potential. These findings indicate that chronic exposure to a HFD negatively affects the bioenergetics of liver mitochondria and this probably contributes to hypoxic stress and deleterious NO-dependent modification of mitochondrial proteins.

Show MeSH
Related in: MedlinePlus