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.
3. Progress Report
We investigated the efficacy of an equivalent dosage of dietary carotenoid lycopene from either a pure compound or a tomato extract against high fat diet-induced liver inflammation called nonalcoholic steatohepatitis (NASH) in a rat model. Results showed that both lycopene and tomato extract supplementations significantly decreased several biomarkers of liver cancer development in the livers of high fat diet-fed rats. An interesting finding in this study is that tomato extract, not lycopene, displayed an efficacy to protect against high fat diet-induced liver inflammation. Using the same rat model, we substituted alcohol for a small portion of carbohydrates while maintaining equal total fat and calorie intake (isocaloric) between the high fat diet and alcohol-fed rats. We observed that moderate consumption of alcohol in those with the pre-existing nonalcoholic steatohepatitis condition led to more hepatic inflammation and cellular apoptosis. Our results indicate that subjects with NASH should use great caution in consuming alcohol, even at a moderate level. In addition, we observed that there was massive hepatic steatosis, alcoholic foamy degeneration with a mixed infiltrate of inflammatory cells, and liver tumor detected in ethanol-fed rats at ten months, Furthermore, we demonstrated lower vitamin A status and higher expression of hepatic carotenoid cleavage enzymes expression in the ethanol fed rats. Our studies indicate that chronic alcohol intake induced liver tumor formation is related to impairment of vitamin A metabolism. Xanthophyll carotenoids, such as lutein, zeaxanthin and beta cryptoxanthin, may provide potential health benefits in humans against chronic and degenerative diseases. We investigated carotenoid excentric break-down enzyme activity towards the carotenoid substrates zeaxanthin, lutein and beta cryptoxanthin using ferret carotenoid cleavage enzyme. We identified both volatile and non-volatile apocarotenoid products indicating a key role of carotenoid excentric break-down enzyme in xanthophylls carotenoid metabolism. Since apo-carotenoids serve as important signaling molecules in a variety of biological processes, our study indicates that the enzymatic cleavage of xanthophylls by mammalian carotenoid excentric breakdown enzyme represents a new avenue of research regarding vertebrate carotenoid metabolism and biological function. We evaluated the effects of dietary carotenoid beta cryptoxanthin enriched in orange and orange juice, mango, and red pepper on cigarette smoke-induced precancerous lesions, inflammation, and smoke-induced oxidative DNA damage in the lung tissue of ferrets. We found that cigarette smoke exposure lowered plasma and lung beta cryptoxanthin levels. beta cryptoxanthin significantly decreased smoke-induced lung precancerous lesion (squamous metaplasia) and inflammation. Beta cryptoxanthin also substantially reduced smoke-elevated TNF-alpha levels in alveolar, bronchial, bronchiolar and bronchial serous/mucous gland epithelial cells and in lung macrophages. Moreover, beta cryptoxanthin decreased smoke-induced oxidative NDA damage.
1. Tomato possesses anti-inflammatory activity. One of the consequences of the current obesity epidemic is an increased prevalence of nonalcoholic fatty liver disease (e.g., nonalcoholic steatohepatitis), which has paralleled the increased incidence of liver cancer in the USA. ARS-funded researchers at JMUSDA-HNRCA at Tufts University, Boston, MA, provided strong evidence demonstrating that tomato extract supplementation is protective against high fat diet-induced inflammation and the development of preneoplastic lesions in the livers. The potential mechanism underlying the anti-inflammatory efficacy manifested by tomato extract is most likely due to a combined or synergistic effect of multiple constituents in tomatoes (e.g., tocopherols, phytoene and phytofluene). This project generated a great interest in role of nutrition in the cancer prevention field to study whether and how tomato extract prevent high fat diet/obesity related insulin resistance, oxidative stress, inflammation and cancers. These data show a high potential of tomato extract in cancer prevention.
2. New pathway of non-provitamin A carotenoid metabolism is discovered: It is acknowledged that for provitamin A carotenoids, such as, beta-carotene, central cleavage by carotene 15,15’- oxygenase is a major pathway leading to vitamin A formation. ARS-funded researchers at JMUSDA-HNRCA at Tufts University, Boston, MA, demonstrated that excentric cleavage of the carotenoid molecule by carotene-9’,10’-oxygenase, is a major metabolic pathway for non-provitamin A carotenoids, such as lutein and lycopene. This work identified a new role of non-provitamin A carotenoids in cancer prevention and opened a new avenue in carotenoid research in mammals.
3. Beta cryptoxanthin is an effective preventive agent against smoke-induced lung inflammation. To determine if carotenoids other than beta carotene may account for the protective effects of fruits and vegetables on lung cancer risk seen in observational studies, ARS-funded researchers at JMUSDA-HNRCA at Tufts University, Boston, MA, demonstrated that one specific carotenoid, beta cryptoxanthin, was significantly associated with reduced risk of lung cancer among smokers. Our studies both in vivo and in vitro also support the notion that the beneficial effects of beta cryptoxanthin in smokers is unique and beta cryptoxanthin is an effective preventive agent, rather than beta carotene or other carotenoids. These findings have significant impact on cancer prevention strategies.