Limits...
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.

Show MeSH

Related in: MedlinePlus

Effect of HFD on 3-NT levels in liver(A) Representative photomicrographs depicting patterns of 3-NT staining (brown) against a haematoxylin nuclear counterstain (blue) in liver sections of mice fed either a control diet or HFD for 16 weeks. Increased brown staining demonstrates increased tissue 3-NT levels in the HFD group as compared with control. Image analysis demonstrated increased area (B) and intensity (C) of 3-NT staining in liver from the HFD group compared with control. Values represent the means±S.E.M. for five pairs of mice. *P<0.05, compared with control.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2637578&req=5

Figure 7: Effect of HFD on 3-NT levels in liver(A) Representative photomicrographs depicting patterns of 3-NT staining (brown) against a haematoxylin nuclear counterstain (blue) in liver sections of mice fed either a control diet or HFD for 16 weeks. Increased brown staining demonstrates increased tissue 3-NT levels in the HFD group as compared with control. Image analysis demonstrated increased area (B) and intensity (C) of 3-NT staining in liver from the HFD group compared with control. Values represent the means±S.E.M. for five pairs of mice. *P<0.05, compared with control.

Mentions: NO-dependent inhibition of respiration has been shown to increase superoxide (O2●−) production from the respiratory chain and in turn could lead to greater levels of peroxynitrite (ONOO−) formation [26]. This oxidant can modify proteins in the respiratory chain, leading to decreased activity [27]. Interestingly, nitration of tyrosine has been reported to be increased in the livers of NASH patients [28] and ob/ob mice with severe steatosis [29]. Similarly, iNOS levels are increased in liver of ob/ob mice; however, the impact of a HFD on hepatic iNOS expression is not known. While iNOS protein was detected in control livers, significantly higher levels of iNOS protein were detected in livers of HFD mice at 16 weeks (Figure 6). In concert, we examined the effect of feeding a HFD on 3-NT formation. A small amount of 3-NT was detected in livers from control animals, whereas there was significant 3-NT staining in the livers of mice fed the HFD for 16 weeks (Figure 7A). Both the area and intensity of 3-NT staining were significantly increased in response to a HFD compared with control (Figures 7B and 7C). Interestingly, the gradient of 3-NT immunoreactivity parallels that observed for the hypoxia gradient in vivo (Figure 2), suggesting a link between hypoxia and increased nitrative stress. Moreover, as predicted, 3-NT levels were elevated within mitochondrial proteins isolated from livers of the HFD group compared with controls (Figure 8).


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 3-NT levels in liver(A) Representative photomicrographs depicting patterns of 3-NT staining (brown) against a haematoxylin nuclear counterstain (blue) in liver sections of mice fed either a control diet or HFD for 16 weeks. Increased brown staining demonstrates increased tissue 3-NT levels in the HFD group as compared with control. Image analysis demonstrated increased area (B) and intensity (C) of 3-NT staining in liver from the HFD group compared with control. Values represent the means±S.E.M. for five pairs of mice. *P<0.05, compared with control.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Effect of HFD on 3-NT levels in liver(A) Representative photomicrographs depicting patterns of 3-NT staining (brown) against a haematoxylin nuclear counterstain (blue) in liver sections of mice fed either a control diet or HFD for 16 weeks. Increased brown staining demonstrates increased tissue 3-NT levels in the HFD group as compared with control. Image analysis demonstrated increased area (B) and intensity (C) of 3-NT staining in liver from the HFD group compared with control. Values represent the means±S.E.M. for five pairs of mice. *P<0.05, compared with control.
Mentions: NO-dependent inhibition of respiration has been shown to increase superoxide (O2●−) production from the respiratory chain and in turn could lead to greater levels of peroxynitrite (ONOO−) formation [26]. This oxidant can modify proteins in the respiratory chain, leading to decreased activity [27]. Interestingly, nitration of tyrosine has been reported to be increased in the livers of NASH patients [28] and ob/ob mice with severe steatosis [29]. Similarly, iNOS levels are increased in liver of ob/ob mice; however, the impact of a HFD on hepatic iNOS expression is not known. While iNOS protein was detected in control livers, significantly higher levels of iNOS protein were detected in livers of HFD mice at 16 weeks (Figure 6). In concert, we examined the effect of feeding a HFD on 3-NT formation. A small amount of 3-NT was detected in livers from control animals, whereas there was significant 3-NT staining in the livers of mice fed the HFD for 16 weeks (Figure 7A). Both the area and intensity of 3-NT staining were significantly increased in response to a HFD compared with control (Figures 7B and 7C). Interestingly, the gradient of 3-NT immunoreactivity parallels that observed for the hypoxia gradient in vivo (Figure 2), suggesting a link between hypoxia and increased nitrative stress. Moreover, as predicted, 3-NT levels were elevated within mitochondrial proteins isolated from livers of the HFD group compared with controls (Figure 8).

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