Liver steatosis and redox status alterations in obese Zucker rats

Abstract

Obesity in the United States and other developed countries has been at epidemic proportions for more than two decades and continues to grow. The obese population has high comorbidity and mortality rates due to a variety of chronic diseases including cancer. The development of liver steatosis is a common consequence. This disease, ranging from simple hepatic steatosis and nonalcoholic steatohepatitis to cirrhosis, is a major health problem in the USA and worldwide. The negative effect of liver steatosis is recognized by its significant impact on the metabolic profile in humans. Our previous results demonstrated that obesity in Zucker rats was accompanied with an increase of oxidative and nitrosative stress in liver, perturbation of methylation (SAM/SAH) ratio and significant morphological changes in liver: increase in fatty steatosis to small foci of mononuclear infiltration. However, metabolic details that are leading to these changes in liver of obese rats are less known. Therefore, the objective of this study was to investigate the possible mechanisms that create such metabolic abnormalities. After one week of acclimation, six‐week old female lean (n=26) and obese (n=20) Zucker rats were fed AIN‐93 G diet and sacrificed 155 days later. Liver samples were snap frozen in liquid nitrogen and stored at −80° C until later. We used high sensitivity HPLC‐ECD and LC‐MS methods to assess the metabolic profile related to the methionine cycle and oxidative and nitrosative stress. Our results show that obese rats had significantly higher levels of essential amino acid Methionine (P<0.0001) and free Homocysteine (P<0.01) but lover level of free Cysteine (P<0.01) compared to lean rats. In contrast, the Cystine (oxidized Cysteine) and the Cystine/Cysteine (oxidative stress ratio), was significantly higher in obese rats (P <0.01 and P<0.001 respectfully) compared to lean rats. Additionally, obesity caused a significant (P<0.01) drop in liver HADPH/HADP ratio (redox ratio) and significant (P<0.02) drop in fHomocysteine/Methylation (methylation ratio). In summary, higher levels of oxidative/nitrosative stress in the liver of obese Zucker rats are the results of complex metabolic processes which include decreased levels of free reduced Cysteine as rate limiting amino acid in de‐novo Glutathione (GSH) synthesis; decreased reduction capacity (NADPH/NADP ratio) in liver what leads to lower rate of free Glutathione restoration from oxidized form (GSSG); increased intracellularly level of oxidized (GSSG, Cystine) products; reduction of methylation reactions activities (Homocysteine/Methionine ratio).Support or Funding InformationArkansas Biosicence Institute to RH and SM.