Alcohol,nutrition and liver cancer:Role of Toll-like receptor signaling

This article reviews the evidence that ties the development of hepatocellular carcinoma (HCC) to the natural immune pro-inflammatory response to chronic liver disease, with a focus on the role of Toll-like receptor (TLR) signaling as the mechanism of liver stem cell/progenitor transformation to HCC. Two exemplary models of this phenomenon are reviewed in detail. One model applies chronic ethanol/lipopolysaccharide feeding to the activated TLR4 signaling pathway. The other applies chronic feeding of a carcinogenic drug, in which TLR2 and 4 signaling pathways are activated. In the drug-induced model, two major methyl donors, S-adenosylmethionine and betaine, prevent the upregulation of the TLR signaling pathways and abrogate the stem cell/progenitor proliferation response when fed with the carcinogenic drug. This observation supports a nutritional approach to liver cancer prevention and treatment. The observation that upregulation of the TLR signaling pathways leads to liver tumor formation gives evidence to the popular concept that the chronic pro-inflammatory response is an important mechanism of liver oncogenesis. It provides a nutritional approach, which could prevent HCC from developing in many chronic liver diseases.

Hepatitis D and hepatocellular carcinoma

Hepatitis D virus(HDV) is a defective circular shape single stranded HDV RNA virus with two types of viral proteins,small and large hepatitis D antigens,surrounded by hepatitis B surface antigen.Superinfection with HDV in chronic hepatitis B is associated with a more threatening form of liver disease leading to rapid progression to cirrhosis.In spite of some controversy in the epidemiological studies,HDV infection does increase the risk of hepatocellular carcinoma(HCC) compared to hepatitis B virus(HBV) monoinfection.Hepatic decompensation,rather than development of HCC,is the first usual clinical endpoint during the course of HDV infection.Oxidative stress as a result of severe necroinflammation may progress to HCC.The large hepatitis D antigen is a regulator of various cellular functions and an activator of signal transducer and activator of transcription(STAT)3 and the nuclear factor kappa B pathway.Another proposed epigenetic mechanism by which HCC may form is the aberrant silencing of tumor suppressor genes by DNA Methyltransferases.HDV antigens have also been associated with increased histone H3 acetylation of the clusterin promoter.This enhances the expression of clusterin in infected cells,increasing cell survival potential.Any contribution of HBV DNA integration with chromosomes of infected hepatocytes is not clear at this stage.The targeted inhibition of STAT3 and cyclophilin,and augmentation of peroxisome proliferatoractivated receptor γ have a potential therapeutic role in HCC.