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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 liver histology, triacylglycerol measurements and CYP2E1 protein levelsRepresentative liver sections from mice maintained for 16 weeks on control (A, 20×) or a HFD (B, 20× and C, 40×). (C) Ballooned hepatocytes (three solid arrows) and Mallory bodies (one broken arrow) were observed in zone 3 of HFD-fed mouse livers. (D) Quantification of liver triacylglycerol content. P=0.07, compared with control at 8 weeks; *P<0.05, compared with control at 16 weeks. (E) Quantification of CYP2E1 protein levels. Representative Western blots from each group are shown above the bar graph in (E). Levels of immunoreactive CYP2E1 protein were normalized to total protein run on duplicate gels stained with SyproRuby protein stain (Invitrogen). *P<0.05, compared with control at 8 weeks; **P<0.01, compared with control at 8 weeks; ***P<0.01, compared with HFD at 8 weeks. (F) Quantification of total protein on duplicate protein-stained gels used for CYP2E1 Western blots. Note there were no differences in total protein between control and HFD groups. Values represent the means±S.E.M. for 4–6 pairs of mice.
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Figure 1: Effect of HFD on liver histology, triacylglycerol measurements and CYP2E1 protein levelsRepresentative liver sections from mice maintained for 16 weeks on control (A, 20×) or a HFD (B, 20× and C, 40×). (C) Ballooned hepatocytes (three solid arrows) and Mallory bodies (one broken arrow) were observed in zone 3 of HFD-fed mouse livers. (D) Quantification of liver triacylglycerol content. P=0.07, compared with control at 8 weeks; *P<0.05, compared with control at 16 weeks. (E) Quantification of CYP2E1 protein levels. Representative Western blots from each group are shown above the bar graph in (E). Levels of immunoreactive CYP2E1 protein were normalized to total protein run on duplicate gels stained with SyproRuby protein stain (Invitrogen). *P<0.05, compared with control at 8 weeks; **P<0.01, compared with control at 8 weeks; ***P<0.01, compared with HFD at 8 weeks. (F) Quantification of total protein on duplicate protein-stained gels used for CYP2E1 Western blots. Note there were no differences in total protein between control and HFD groups. Values represent the means±S.E.M. for 4–6 pairs of mice.

Mentions: Mice were fed a control diet or HFD in a pair-fed isocaloric fashion for 8 or 16 weeks. Livers from mice on the control diet exhibited no pathology (Figure 1A). These findings are in agreement with those from previous studies conducted by our laboratories using the same control liquid diet [17]. In contrast, livers from mice fed a HFD showed an accumulation of macro- and micro-vesicular fat at both the 8 (results not shown) and 16 week time points (Figure 1B), which was associated with increased liver triacylglycerol content (Figure 1D) and CYP2E1 protein (Figure 1E) as compared with controls. Steatosis was accompanied by hepatocyte ballooning and Mallory bodies in zone 3 of the liver lobule (Figure 1C), which are hallmark features of NASH. These results are consistent with earlier observations from Lieber et al. [21], who reported the development of NASH-like features in rats fed the same HFD.


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 liver histology, triacylglycerol measurements and CYP2E1 protein levelsRepresentative liver sections from mice maintained for 16 weeks on control (A, 20×) or a HFD (B, 20× and C, 40×). (C) Ballooned hepatocytes (three solid arrows) and Mallory bodies (one broken arrow) were observed in zone 3 of HFD-fed mouse livers. (D) Quantification of liver triacylglycerol content. P=0.07, compared with control at 8 weeks; *P<0.05, compared with control at 16 weeks. (E) Quantification of CYP2E1 protein levels. Representative Western blots from each group are shown above the bar graph in (E). Levels of immunoreactive CYP2E1 protein were normalized to total protein run on duplicate gels stained with SyproRuby protein stain (Invitrogen). *P<0.05, compared with control at 8 weeks; **P<0.01, compared with control at 8 weeks; ***P<0.01, compared with HFD at 8 weeks. (F) Quantification of total protein on duplicate protein-stained gels used for CYP2E1 Western blots. Note there were no differences in total protein between control and HFD groups. Values represent the means±S.E.M. for 4–6 pairs of mice.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 1: Effect of HFD on liver histology, triacylglycerol measurements and CYP2E1 protein levelsRepresentative liver sections from mice maintained for 16 weeks on control (A, 20×) or a HFD (B, 20× and C, 40×). (C) Ballooned hepatocytes (three solid arrows) and Mallory bodies (one broken arrow) were observed in zone 3 of HFD-fed mouse livers. (D) Quantification of liver triacylglycerol content. P=0.07, compared with control at 8 weeks; *P<0.05, compared with control at 16 weeks. (E) Quantification of CYP2E1 protein levels. Representative Western blots from each group are shown above the bar graph in (E). Levels of immunoreactive CYP2E1 protein were normalized to total protein run on duplicate gels stained with SyproRuby protein stain (Invitrogen). *P<0.05, compared with control at 8 weeks; **P<0.01, compared with control at 8 weeks; ***P<0.01, compared with HFD at 8 weeks. (F) Quantification of total protein on duplicate protein-stained gels used for CYP2E1 Western blots. Note there were no differences in total protein between control and HFD groups. Values represent the means±S.E.M. for 4–6 pairs of mice.
Mentions: Mice were fed a control diet or HFD in a pair-fed isocaloric fashion for 8 or 16 weeks. Livers from mice on the control diet exhibited no pathology (Figure 1A). These findings are in agreement with those from previous studies conducted by our laboratories using the same control liquid diet [17]. In contrast, livers from mice fed a HFD showed an accumulation of macro- and micro-vesicular fat at both the 8 (results not shown) and 16 week time points (Figure 1B), which was associated with increased liver triacylglycerol content (Figure 1D) and CYP2E1 protein (Figure 1E) as compared with controls. Steatosis was accompanied by hepatocyte ballooning and Mallory bodies in zone 3 of the liver lobule (Figure 1C), which are hallmark features of NASH. These results are consistent with earlier observations from Lieber et al. [21], who reported the development of NASH-like features in rats fed the same HFD.

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