DIETARY COCOA (THEOBROMA CACAO) SUPPLEMENTATION IMPROVES OBESITY-RELATED FATTY LIVER DISEASE IN MICE

Open Access
Author:
Sun, Mingyao
Graduate Program:
Food Science
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 02, 2016
Committee Members:
  • Joshua D. Lambert, Dissertation Advisor
  • Joshua D. Lambert, Committee Chair
  • Jairam K.P. Vanamala, Committee Member
  • Gregory R. Ziegler, Committee Member
  • Gregory Shearer, Outside Member
Keywords:
  • Cocoa
  • Non-alcoholic fatty liver disease
  • Lipid metabolism
  • Mitochondrial biogenesis
  • Oxidative stress
  • Inflammation
Abstract:
Nonalcoholic Fatty Liver Disease (NAFLD), defined in 1980s, is a liver disease that histologically mimics alcoholic hepatitis but occurs in individuals who do not abuse alcohol. NAFLD is an increasingly recognized condition that may progress to end-stage liver disease; it can be characterized by fat accumulation in liver exceeding 5–10% by weight. NAFLD is classified into two stages: simple fatty liver (i.e. steatosis) and non-alcoholic steatohepatitis (NASH). The later stage, NASH, has drawn more cautions because its can evolve to more advanced liver damage, and cannot be treated effectively so far. “Two hit hypothesis” has been proposed to explain the progression from simple steatosis to NASH. According to this hypothesis, steatosis is the “first hit” which increases the vulnerability of the liver to various “second hits” such as chronic inflammation, oxidative damage, mitochondrial dysfunction, that in turn lead to the inflammation, fibrosis and cellular death characteristic of NASH. It is expectable that food components targeting at those “second hits” have therapeutic properties and may help prevent the pathogenesis process of NASH. Cocoa (or cacao) is a product of Theobroma cacao fruit, which grows in the equatorial tropics including Central and South America, West Africa, and Malaysia. Cocoa has a long history in use, to treat numbers of disorders such as angina and heart pain. Recent studies has confirmed various health-beneficial effects associated with cocoa products including their multifactorial ability to modulate immune response, and anti-inflammatory, anti-radical and anti-carcinogenic properties. Considering the pathogenesis of NAFLD and NASH, the multifactorial effects of cocoa may make it a promising candidate in preventing obesity-related fatty liver disease. To study the protective effect of cocoa, a high-fat-diet (HFD)-fed C57BL/6J mouse model is applied. This model is advantageous to investigate metabolic fatty liver disease due to two reasons. Firstly, steatosis developed in healthy livers. Secondly, after steatosis, inflammatory process is triggered by release of proinflammatory cytokines and oxidative stress that lead to hepatocyte apoptosis. This model allows observing the pathogenesis from simple steatosis to NASH. In experiments, mice were fed with high fat diet (60% calorie from fat) for 8 weeks to induce steatosis. After 8 weeks, mice were randomly divided into two groups: HF-HFC and HF group. In HF diet mice still maintain high fat diet for additional 10 weeks, whereas in HF-HFC mice were treated with 8% cocoa supplemented with high fat diet. In this research, we hypothesized that cocoa supplementation can ameliorate obesity related NAFLD through modulating lipid metabolism pathway, boosting endogenous antioxidant defense capacity, enhancing mitochondria biogenesis, and reducing chronic inflammation in mice. To test our hypothesis, we proposed three specific aims: Specific Aim 1: Evaluation of protective effect of cocoa supplementation on hepatic lipid metabolism pathway in mice model of NAFLD (discussed in chapter 2). Specific Aim 2: Evaluation of protective effect of cocoa supplementation on hepatic oxidative stress and mitochondrial function in mice model of NAFLD (discussed in chapter 3). Specific Aim 3: Evaluation of protective effect of cocoa supplementation on liver Kupffer cell differentiation in mice model of NAFLD (discussed in chapter 4). In chapter 2, we demonstrate that cocoa-treated obese mice decrease triglycerides (TAG), an important diagnostic marker of NAFLD, by enhancing fatty acid disposal and reducing lipogenesis in the liver. In chapter 3, we demonstrate that the beneficial effects of cocoa supplementation on NAFLD is through increasing mitochondrial biogenesis and related antioxidant response signaling. In chapter 4, we demonstrated that dietary cocoa is able to alternatively activate M2 KCs in HF-fed mice, and this phenotypic switch protects mice from ongoing of liver damage compared with HF treated alone. In conclusion, in this dissertation, we demonstrated that cocoa supplementation did mitigate obesity-related fatty liver disease, and could be useful in preventing the progression of hepatic steatosis to NASH. These effects are caused by three mechanisms: modulating lipid metabolism pathway, boosting endogenous antioxidant defense capacity, increasing mitochondria biogenesis and reduce chronic inflammation. It is clear that dietary cocoa could be a potential dietary intervention to modulate obesity-related fatty liver disease.