Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Nikam, A.
Transition between Acute and Chronic Oxidative Liver Damage in a Mouse Model for Nonalcoholic Steatohepatitis
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Medical University of Graz; 2014. pp. 120
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- Autor*innen der Med Uni Graz:
- Nikam Aniket Popatrao
- Betreuer*innen:
- Abuja Peter Michael
- Höfler Gerald
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- Abstract:
- Oxidative stress and mitochondrial dysfunction are presumed to play a major role in the pathogenesis of various chronic degenerative liver diseases in humans such as alcoholic and non-alcoholic steatohepatitis, and hepatocellular carcinoma (HCC). Nonalcoholic steatohepatitis (NASH) is an inflammatory liver disease with unfavorable prognosis characterized by fat accumulation and chronic hepatocyte damage, resulting from massive metabolic changes and oxidative stress originating probably from mitochondria. The formation of hepatocyte protein inclusions i.e., Mallory-Denk bodies (MDBs) in response to chronic liver injury has become one of the major morphological hallmark of this disease. Here we report results obtained with a mouse model for NASH obtained by feeding mice 3,5-diethoxycarbonyl-1,4- dihydrocollidine, DDC, for up to 10 weeks. Hepatotoxicity was induced in male Swiss Albino mice by a diet containing 0.1% DDC. This leads to development of morphologically well-characterized hepatocellular damage involving formation of protein aggregates and inflammation. In this study we characterized the model in terms of evolution of oxidative and metabolic damage observed from impaired energy metabolism during the progression from initial, acute damage to the chronic intoxication phenotype. As human metabolic liver disease is characterized specifically by alterations in lipid metabolism, we additionally investigated the role of PPARa in the development of chronic liver disease induced by DDC in mice. Body weight change and serum liver enzyme activities were determined, together with morphologic alterations in livers, induction of antioxidant response (Nrf2, HO- 1), oxidative damage and ATP content. Liver mitochondria were prepared and respiration, oxidative damage in the mitochondrial fraction and the presence of mitochondrial HO-1 (mtHO-1) were measured. Concomitantly, we also observed Cyp2a5 expression strongly increased, in parallel to induction of Nrf2 and other Nrf2-dependent enzymes. Both HO-1 and Cyp2a5 were found to be increasingly localized in the inner mitochondrial membrane during the development of the chronic stage. We also observed that short-term intoxication with DDC led to acute liver toxicity with significant downregulation of PPARa and associated genes. This downregulation persisted through long-term stages of intoxication when the characteristic morphologic phenotype resembles that of human steatohepatitis. PPARa is known to be a ligand-dependent transcription factor and fibrates are well known agonist for PPARa. Fenofibrate has been reported to have beneficial effect on lipid metabolism through activation of PPARa activation. The succeeding studies have shown that PPARa plays a critical role in regulating the enzymes involved in lipid metabolism and inflammation by diverse mechanisms. In the DDC model, fenofibrate prevented the extreme downregulation of PPARa and associated genes involved in lipid metabolism and the development of the chronic phenotype. In addition, PPARa modulated the expression of redox-regulating genes. Our findings reveal a qualitative difference of the damage between the initial (acute) intoxication stage, and long-term (chronic) intoxication. Oxidative damage precedes mitochondrial dysfunction in our model, and continues over the whole duration of the experiment. After the acute intoxication stage, adaptive responses involving mtHO-1 are induced, leading to improved respiration and preventing further reduction of ATP levels. In addition, PPARa appears to be a major modulator of metabolic and oxidative stress in the DDC model of chronic hepatocellular damage. The chronic phenotype probably represents an adaptive process preserving essential liver functions for a considerable time, in contrast to acute liver toxicity models.