Role of alcohol metabolism in non-alcoholic steatohepatitis - PubMed (original) (raw)

Role of alcohol metabolism in non-alcoholic steatohepatitis

Susan S Baker et al. PLoS One. 2010.

Abstract

Background: Non-alcoholic steatohepatitis (NASH) is a serious form of non-alcoholic fatty liver disease (NAFLD), associated with obesity and insulin resistance. Previous studies suggested that intestinal bacteria produced more alcohol in obese mice than lean animals.

Methodology/principal findings: To investigate whether alcohol is involved in the pathogenesis of NASH, the expression of inflammation, fibrosis and alcohol metabolism related genes in the liver tissues of NASH patients and normal controls (NCs) were examined by microarray (NASH, n = 7; NC, n = 4) and quantitative real-time PCR (NASH, n = 6; NC, n = 6). Genes related to liver inflammation and fibrosis were found to be elevated in NASH livers compared to normal livers. The most striking finding is the increased gene transcription of alcohol dehydrogenase (ADH) genes, genes for catalase and cytochrome P450 2E1, and aldehyde dehydrogenase genes. Immunoblot analysis confirmed the increased expression of ADH1 and ADH4 in NASH livers (NASH, n = 9; NC, n = 4).

Conclusions/significance: The augmented activity of all the available genes of the pathways for alcohol catabolism suggest that 1) alcohol concentration was elevated in the circulation of NASH patients; 2) there was a high priority for the NASH livers to scavenge alcohol from the circulation. Our data is the first human evidence that suggests alcohol may contribute to the development of NAFLD.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. Quantitative RT-PCR analysis of CXCL10 in NASH livers and normal controls (NCs).

Quantitative RT-PCR analysis were performed as described in Methods. CXCL10 and GAPD (house-keeping gene) specific primer pairs are specified in Table 2. The complementary DNAs prepared from NASH livers (n = 6) and NCs (n = 6) were analyzed in duplicate. CXCL10 expression level of each sample was normalized with that of GAPD. Sample means of the CXCL10 gene expression levels were plotted with error bars indicating the standard errors.

Figure 2

Figure 2. Quantitative RT-PCR analysis with NASH livers and NCs.

Gene expression levels of (A) ADH1C, (B) ADH4, (C) ADH6, (D) ALDH2, (E) ALDH8A1 and (F) TLR4 were examined by qRT-PCR as described in Methods. The complementary DNAs prepared from NASH livers (n = 6) and NCs (n = 6) were analyzed in duplicate. PCR primer pairs are specified in Table 2. Gene expression levels of each sample were normalized with those of GAPD. Sample means were plotted with error bars indicating the standard errors.

Figure 3

Figure 3. Elevated expression of ADH1 and ADH4 proteins in NASH livers.

(A) Western blot analyses were performed with lysates prepared from NASH livers and NCs. The NCs were of normal BMI and free from steatosis. Separate blots were probed for ADH1, ADH4 and β-actin as these proteins all migrate at about 43 kDa. While similar signals for actin were detected for all samples, the NASH livers exhibited stronger signals for both ADH1 and ADH4. (B) The Western blot results were quantitated with NIHimage software. The normalized quantities of the ADH1 and ADH4 signals were the densities of the ADH bands divided by that of the β-actin bands, respectively. The mean values for NASH and NC were plotted with error bars representing the standard errors of the means.

Figure 4

Figure 4. The alcohol hypothesis of non-alcoholic liver diseases.

Non-alcoholic fatty liver diseases are commonly associated with obesity. In addition to the well-known mechanisms that obesity leads to steatosis via insulin resistance, and obesity related bacteria facilitate liver inflammation, the gene transcription data reported here support a central role for alcohol in the pathogenesis of NAFLD. Overgrowth of alcohol-producing bacteria in the intestine of obese patients likely causes increased alcohol in the circulation, which in turn induced the expression of genes for alcohol catabolism, including ADH and cytochrome P450 2E1. The increased activity of ADH results in the elevated level of NADH, which favors fatty acid synthesis and opposes its break down, leading to steatosis; the elevated P450 2E1 could generate excessive ROS, a known cause for liver inflammation.

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