DNA methylation of angiotensin II receptor gene in nonalcoholic steatohepatitis-related liver fibrosis

Effect of combined farnesoid X receptor agonist and angiotensin II type 1 receptor blocker on ongoing hepatic fibrosis

OBJECTIVE

Nonalcoholic steatohepatitis (NASH) is difficult to diagnose in patients with no symptoms. We aimed to investigate the combined effect of farnesoid X receptor (FXR) agonist, obeticholic acid (OCA), and angiotensin II type 1 receptor blocker (ARB: losartan) on an ongoing hepatic fibrosis in a NASH rat model.

METHODS

Fischer 344 rats were fed with choline-deficient L-amino-acid-defined (CDAA) diet for 16 weeks. After 8-week administration of CDAA diet, OCA, losartan, or a combination of these drugs was administered at a dose of 30 mg/kg/day for 8 weeks by oral gavage. The in vivo and in vitro effects of OCA + losartan and liver fibrosis progression, lipopolysaccharide (LPS), Toll-like receptor 4 (TLR4) regulatory cascade, and gut barrier function were evaluated.

RESULTS

OCA + losartan alleviated hepatic fibrosis progression by suppressing α-SMA expression. It inhibited the proliferation of activated hepatic stellate cell (Ac-HSC) and mRNA expression of hepatic transforming growth factor-β1 (TGF-β1), TLR4, and tissue inhibitor of metalloproteinase-1 (TIMP-1) and decreased the hydroxyproline levels. OCA increased the hepatic matrix metalloproteinase-2 (MMP-2) mRNA expression. OCA decreased the mRNA expression of hepatic LPS-binding protein and intestinal permeability by ameliorating the disruption of CDAA diet-induced zonula occludens-1. Losartan directly inhibited the proliferation of Ac-HSC. The in vitro suppressive effects of OCA + losartan on the mRNA expressions of TGF-β1 and α1(I)-procollagen, TLR4, and TIMP-1 in Ac-HSCs were almost in parallel.

CONCLUSIONS

OCA + losartan suppressed the ongoing hepatic fibrosis by attenuating gut barrier dysfunction and suppressing Ac-HSC proliferation. Combined therapy may be a promising novel approach for NASH with fibrosis.

Epigenetic regulation in fibrosis progress

Fibrosis, a common process of chronic inflammatory diseases, is defined as a repair response disorder when organs undergo continuous damage, ultimately leading to scar formation and functional failure. Around the world, fibrotic diseases cause high mortality, unfortunately, with limited treatment means in clinical practice. With the development and application of deep sequencing technology, comprehensively exploring the epigenetic mechanism in fibrosis has been allowed. Extensive remodeling of epigenetics controlling various cells phenotype and molecular mechanisms involved in fibrogenesis was subsequently verified. In this review, we summarize the regulatory mechanisms of DNA methylation, histone modification, noncoding RNAs (ncRNAs) and N6-methyladenosine (m6A) modification in organ fibrosis, focusing on heart, liver, lung and kidney. Additionally, we emphasize the diversity of epigenetics in the cellular and molecular mechanisms related to fibrosis. Finally, the potential and prospect of targeted therapy for fibrosis based on epigenetic is discussed.

Hydralazine Sensitizes to the Antifibrotic Effect of 5-Aza-2'-deoxycytidine in Hepatic Stellate Cells

BACKGROUND

Hepatic stellate cell (HSC) activation is essential for the development of liver fibrosis. Epigenetic machinery, such as DNA methylation, is largely involved in the regulation of gene expression during HSC activation. Although the pharmacological DNA demethylation of HSC using 5-aza-2'-deoxycytidine (5-aza-dC) yielded an antifibrotic effect, this drug has been reported to induce excessive cytotoxicity at a high dose. Hydralazine (HDZ), an antihypertensive agent, also exhibits non-nucleoside demethylating activity. However, the effect of HDZ on HSC activation remains unclear. In this study, we performed a combined treatment with 5-aza-dC and HDZ to obtain an enhanced antifibrotic effect with lower cytotoxicity.

METHODS

HSC-T6 cells were used as a rat HSC cell line in this study. The cells were cultivated together with 1 µM 5-Aza-dC and/or 10 µg/mL of HDZ, which were refreshed every 24 h until the 96 h treatment ended. Cell proliferation was measured using the WST-1 assay. The mRNA expression levels of peptidylprolyl isomerase A (Ppia), an internal control gene, collagen type I alpha 1 (Cola1), RAS protein activator like 1 (Rasal1), and phosphatase and tensin homolog deleted from chromosome 10 (Pten) were analyzed using quantitative reverse transcription polymerase chain reaction.

RESULTS

The percentage cell viability with 5-aza-dC, HDZ, and combined treatment vs. the vehicle-only control was 101.4 ± 2.5, 95.2 ± 5.7, and 79.2 ± 0.7 (p < 0.01 for 5-aza-dC and p < 0.01 for HDZ), respectively, in the 48 h treatment, and 52.4 ± 5.6, 65.9 ± 3.4, and 29.9 ± 1.3 (p < 0.01 for 5-aza-dC and p < 0.01 for HDZ), respectively, in the 96 h treatment. 5-Aza-dC and the combined treatment markedly decreased Cola1 mRNA levels. Accordingly, the expression levels of Rasal1 and Pten, which are antifibrotic genes, were increased by treatment after the 5-aza-dC and combined treatments. Moreover, single treatment with HDZ did not affect the expression levels of Cola1, Rasal1, or Pten. These results suggest that HDZ sensitizes to the antifibrotic effect of 5-aza-dC in HSC-T6 cells. The molecular mechanism underlying the sensitization to the antifibrotic effect of 5-aza-dC by HDZ remains to be elucidated. The expression levels of rat equilibrative nucleoside transporter genes (rEnt1, rEnt2, and rEnt3) were not affected by HDZ in this study.

CONCLUSIONS

Further confirmation using primary HSCs and in vivo animal models is desirable, but combined treatment with 5-aza-dC and HDZ may be an effective therapy for liver fibrosis without severe adverse effects.