2012 Annual Report
1a.Objectives (from AD-416):
1. Determine whether high fat diet induced non-alcoholic steatohepatitis is a promoting factor in hepatic carcinogenesis.
2. Determine whether dietary lycopene will protect against high fat diet promoted liver cancer development.
1b.Approach (from AD-416):
We will use both high fat diet-induced nonalcoholic steatohepatitis (NASH) rats and genetically-induced obese mice with injections of liver-specific carcinogen,diethylnitrosamine, followed by treatment with tomato extract or lycopene for both short and long durations. We will focus on the role of the stress-activated protein c-Jun-NH2-kinase (JNK) signaling, a key component mediating the high fat-induced oxidative stress and inflammatory processes, in response to tomato extract and lycopene supplementation on both cell proliferation/apoptosis, inflammation and premalignant and malignant lesions in obesity related hepatic tumorigenesis. Wewill complement animal study with cell culture studies (e.g., use siRNA silencing of JNK) using human hepatocyte lines and liver cancer cells to facilitate mechanistic studies to determine the contribution of the JNK signaling pathway to lycopene action. Since adiposity contributes to the increased incidence and/or death from liver cancer, we will examine metabolic alteration, including insulin resistance,and pro-inflammatory signaling in intra-abdominal fat tissue and its potential contribution to hepatic carcinogenesis. Once we establish that there is an association between metabolic alteration and hepatic carcinogenesis, we will examine insulin and insulin growth factors (IGF-I/IGF-II) signaling cascades and address their differential activation in NASH and its related hepatic carcinogenesis, as well as potential actions of tomato extract and lycopene prevention against the onset of high fat diet/obesity-related liver disease.
Fatty liver, which is commonly associated with obesity, is one of the major causes of chronic liver disease. We have demonstrated that lycopene and its metabolite, lycopenoic acid, are beneficial in protecting against high-fat diet induced fatty liver (see accomplishments). In another study, we demonstrated that lycopene supplementation significantly suppressed the growth of colon cancer and its related biomarkers in a mouse model with transplanted tumors. These results suggested that lycopene could act as a chemopreventive agent against the growth and progression of colorectal cancer. Previously we demonstrated that lycopene can be converted into lycopenoic acid by the enzyme called “carotene oxygenase”. Currently we are conducting additional experiments to determine whether the effect of lycopene can be mediated by its breakdown product, lycopenoic acid using the carotene oxygenase knock out mouse model. Previously we showed that the activity of a specific enzyme called SIRT1, which plays a key role in increasing fat oxidation and decreasing fat synthesis, was significantly higher in the lycopenoic acid group as compared with the control group. Thus, we are conducting another study using SIRT1 knockout mice (mice that lack SIRT1) to determine if SIRT1 is a target of lycopenoic acid. The result of this study will generate novel data toward understand the underlying mechanism of lycopene effect on fat metabolism and fatty liver.
Lycopene possesses anti-fatty liver and anti-cancer activity. One of the consequences of the current obesity epidemic is an increased prevalence of fatty liver disease. ARS-funded researchers at the JMUSDA-HNRCA at Tufts University in Boston, Massachusetts, provided strong evidence demonstrating that lycopenoic acid, a breakdown product of the lycopene, is protective against high fat diet-induced fatty liver. For the first time, research has demonstrated that the anti-fatty liver effect of lycopenoic acid was associated with the higher activity of the enzyme called SIRT1, which plays a key role in increasing fat oxidation and decreasing fat synthesis. This data indicates a novel role of the lycopenoic acid in the regulation of lipid metabolism in the liver. These findings have led to greatly increased interest in the role of tomato and tomato products for prevention of obesity associated pathologies, such as utilizing tomato products to prevent high fat diet/obesity related insulin resistance, oxidative stress, inflammation and cancers.