Nuclear Receptor Variants in Liver Disease

This review aims to provide a snapshot of the actual state of knowledge on genetic variants of nuclear receptors (NR) involved in regulating important aspects of liver metabolism. It recapitulates recent evidence for the application of NR in genetic diagnosis of monogenic (“Mendelian”) liver disease and their use in clinical diagnosis. Genetic analysis of multifactorial liver diseases such as viral hepatitis or fatty liver disease identifies key players in disease predisposition and progression. Evidence from these analyses points towards a role of NR polymorphisms in common diseases, linking regulatory networks to complex and variable phenotypes. The new insights into NR variants also offer perspectives and cautionary advice for their use as handles towards diagnosis and treatment

A frequent variant in the human bile salt export pump gene ABCB11 is associated with hepatitis C virus infection, but not liver stiffness in a German population

Background: The human ATP-binding cassette, subfamily B, member 11 (ABCB11) gene encodes the bile salt export pump, which is exclusively expressed at the canalicular membrane of hepatocytes. A frequent variant in the coding region, c.1331 T > C, leading to the amino acid exchange p.V444A, has been associated with altered serum bile salt levels in healthy individuals and predisposes homozygous carriers of the [C] allele for obstetric cholestasis. Recently, elevated bile salt levels were shown to be significantly associated with rates and risk of cirrhosis in patients with chronic hepatitis C virus (HCV) infection treated with pegylated interferon-alpha2 and ribavirin, suggesting a potential role for bile salt levels in HCV treatment outcomes and in the fibrogenic evolution of HCV-related liver disease. The aim of this study was to investigate a possible association of ABCB11 c.1331 T > C with hepatitis C virus (HCV) infection and fibrosis stages as assessed by non-invasive transient elastography in a German cohort of patients. Methods: ABCB11 c.1331 T > C genotype was determined by allelic discrimination assay in 649 HCV infected cases and 413 controls. Overall, 444 cases were staged for fibrotic progression by measurement of liver stiffness. Results: Homo- or heterozygous presence of the frequent [C] allele was associated with HCV positivity (OR = 1.41, CI = 1.02 - 1.95, p = 0.037). No association was detectable between the ABCB11 c.1331 T > C genotype and increased liver stiffness. Conclusions: Our data confirm that homozygous presence of the major [C] allele of ABCB11 c.1331 T > C is a genetic susceptibility factor for HCV infection, but not for liver fibrosis

Altered Expression of Antimicrobial Peptides in the Upper Gastrointestinal Tract of Patients with Diabetes Mellitus

Antimicrobial peptides (AMP) are essential components of innate immunity with a broad range of antimicrobial activities against bacteria, viruses, and fungi. The aim of this study was to investigate AMP expression in the upper gastrointestinal tract in normal and pathological metabolic states in humans. Furthermore, we examined the correlation between vitamin D levels and AMP expression in the same cohort. Serum concentrations of 25-hydroxyvitamin D3 were measured, and mRNA expression of β-defensins HBD-1, -2, -3, -4, α-defensins HD-5 and -6 and cathelicidin in the upper gastrointestinal tract epithelia were determined by quantitative RT-PCR in 31 individuals (10 with type 2 diabetes, 10 with insulin resistance, and 11 healthy controls). The majority of the cohort showed low vitamin D concentrations, which were negatively correlated with mRNA expression levels of HBD-3 in corpus mucosa. HBD-1 and HBD-3 mRNA were expressed in corpus mucosa, with the former significantly decreased in patients with diabetes. Hence, we conclude that type 2 diabetes is associated with reduced AMP expression in the upper gastrointestinal tract, which might contribute towards epithelial barrier dysfunction and increased bacterial translocation in these patients

Hepatic steatosis in patients with acromegaly

Objective Comorbid NAFLD is increasingly being diagnosed in patients with diabetes and nondiabetic endocrinopathies. The aim of this study was to assess hepatic steatosis noninvasively by transient elastography in patients with acromegaly. Design A cross‐sectional study including 22 patients with acromegaly. Methods Hepatic steatosis was quantified using controlled attenuation parameter (CAP) during elastography. Anthropometric measurements were obtained, serum liver function tests and lipid and hormone profiles were measured, and prosteatogenic gene variants were genotyped using standard assays. Results In total, 41% of patients were women (mean age 60 ± 14.7 years, mean BMI 31.2 ± 4.6 kg/m2). Hepatic steatosis, as defined by CAP > 248 dB/m, was present in 66% of patients. Five (45%) of the patients with hepatic steatosis also had fibrosis, and one presented with cirrhosis. Nine patients were carriers of the PNPLA3 p.I148M prosteatogenic [M] risk allele, eight of whom were heterozygotes. CAP values were significantly (P = .045) higher in these patients and corresponded to advanced steatosis, as compared to patients with the wild‐type genotype, who demonstrated CAP values consistent with mild steatosis (311 ± 33 dB/m. vs 254 ± 62 dB/m). CAP values did not differ significantly in carriers of distinct TM6SF2 and MBOAT7 genotypes; however, carriers of the risk alleles displayed higher CAP as compared to wild‐type patients. Conclusions This study shows that in patients with acromegaly, carriers of the PNPLA3 susceptibility allele are at risk of developing hepatic steatosis, as assessed by CAP. Comorbid NAFLD might compound prognosis in such patients; thus, further research into the pathomechanisms and treatment of NAFLD in acromegaly is warranted

MTARC1 and HSD17B13 Variants Have Protective Effects on Non-Alcoholic Fatty Liver Disease in Patients Undergoing Bariatric Surgery

The severity of hepatic steatosis is modulated by genetic variants, such as patatin-like phospholipase domain containing 3 (PNPLA3) rs738409, transmembrane 6 superfamily member 2 (TM6SF2) rs58542926, and membrane-bound O-acyltransferase domain containing 7 (MBOAT7) rs641738. Recently, mitochondrial amidoxime reducing component 1 (MTARC1) rs2642438 and hydroxysteroid 17-beta dehydrogenase 13 (HSD17B13) rs72613567 polymorphisms were shown to have protective effects on liver diseases. Here, we evaluate these variants in patients undergoing bariatric surgery. A total of 165 patients who underwent laparoscopic sleeve gastrectomy and intraoperative liver biopsies and 314 controls were prospectively recruited. Genotyping was performed using TaqMan assays. Overall, 70.3% of operated patients presented with hepatic steatosis. NASH (non-alcoholic steatohepatitis) was detected in 28.5% of patients; none had cirrhosis. The increment of liver fibrosis stage was associated with decreasing frequency of the MTARC1 minor allele (p = 0.03). In multivariate analysis MTARC1 was an independent protective factor against fibrosis ≥ 1b (OR = 0.52, p = 0.03) and ≥1c (OR = 0.51, p = 0.04). The PNPLA3 risk allele was associated with increased hepatic steatosis, fibrosis, and NASH (OR = 2.22, p = 0.04). The HSD17B13 polymorphism was protective against liver injury as reflected by lower AST (p = 0.04) and ALT (p = 0.03) activities. The TM6SF2 polymorphism was associated with increased ALT (p = 0.04). In conclusion, hepatic steatosis is common among patients scheduled for bariatric surgery, but the MTARC1 and HSD17B13 polymorphisms lower liver injury in these individuals

Fibroblast Growth Factor 21 Response in a Preclinical Alcohol Model of Acute-on-Chronic Liver Injury

Background and Aims: Fibroblast growth factor (FGF) 21 has recently been shown to play a potential role in bile acid metabolism. We aimed to investigate the FGF21 response in an ethanol-induced acute-on-chronic liver injury (ACLI) model in Abcb4−/− mice with deficiency of the hepatobiliary phospholipid transporter. Methods: Total RNA was extracted from wild-type (WT, C57BL/6J) and Abcb4−/ − (KO) mice, which were either fed a control diet (WT-Cont and KO-Cont groups; n = 28/group) or ethanol diet, followed by an acute ethanol binge (WT-EtOH and KOEtOH groups; n = 28/group). A total of 58 human subjects were recruited into the study, including patients with alcohol-associated liver disease (AALD; n = 31) and healthy controls (n = 27). The hepatic and ileal expressions of genes involved in bile acid metabolism, plasma FGF levels, and bile acid and its precursors 7α- and 27-hydroxycholesterol (7α- and 27-OHC) concentrations were determined. Primary mouse hepatocytes were isolated for cell culture experiments. Results: Alcohol feeding significantly induced plasma FGF21 and decreased hepatic Cyp7a1 levels. Hepatic expression levels of Fibroblast growth factor receptor 1 (Fgfr1), Fgfr4, Farnesoid X-activated receptor (Fxr), and Small heterodimer partner (Shp) and plasma FGF15/FGF19 levels did not differ with alcohol challenge. Exogenous FGF21 treatment suppressed Cyp7a1 in a dose-dependent manner in vitro. AALD patients showed markedly higher FGF21 and lower 7α-OHC plasma levels while FGF19 did not differ. Conclusions: The simultaneous upregulation of FGF21 and downregulation of Cyp7a1 expressions upon chronic plus binge alcohol feeding together with the invariant plasma FGF15 and hepatic Shp and Fxr levels suggest the presence of a direct regulatory mechanism of FGF21 on bile acid homeostasis through inhibition of CYP7A1 by an FGF15-independent pathway in this ACLI model. Lay Summary: Alcohol challenge results in the upregulation of FGF21 and repression of Cyp7a1 expressions while circulating FGF15 and hepatic Shp and Fxr levels remain constant both in healthy and pre-injured livers, suggesting the presence of an alternative FGF15-independent regulatory mechanism of FGF21 on bile acid homeostasis through the inhibition of Cyp7a1

Common variant p.D19H of the hepatobiliary sterol transporter ABCG8 increases the risk of gallstones in children

Introduction Gallstones are increasingly common in children. Genetic analyses of adult cohorts demonstrated that the sterol transporter ABCG8 p.D19H and Gilbert UGT1A1*28 variants enhance the odds of developing gallstones. The genetic background of common lithiasis in children remains unknown. Methods Overall, 214 children with gallstone disease (1 month–17 years, 107 boys) were inclueded. The control cohorts comprised 214 children (age 6–17 years, 115 boys) and 172 adults (age 40–92 years, 70 men) without gallstones. The ABCG8 p.D19H and UGT1A1*28 polymorphisms as well as ABCB4 (c.504C>T rs1202283, c.711A>T rs2109505) and NPC1L1 variants (p.V1296V rs217434, c.−18C>A rs41279633) were genotyped using TaqMan assays. Serum concentrations of plant sterols and cholesterol precursors were measured by gas chromatography/mass spectrometry. Results The ABCG8 risk allele was associated with an increased risk of stones (OR = 1.82, p = .03). Children carrying the p.19H allele presented with lower serum concentrations of surrogate markers of intestinal cholesterol absorption and decreased ratios of phytosterols to the cholesterol precursor desmosterol. Carriers of the common NPC1L1 rs217434 allele had an increased gallstone risk compared with stone-free adults (OR 1.90, p < .01). This variant also affected the ratio of phytosterols to cholesterol precursors (p = .03). Other tested variants were not associated with gallstone risk. Conclusions The p.D19H ABCG8 and, to a lesser extent, NPC1L1 rs217434 variants increase the risk of early-onset gallstone formation. These results point to the presence of a common lithogenic pathway in children and adults

Incidental findings on brain magnetic resonance imaging: systematic review and meta-analysis

Objective To quantify the prevalence of incidental findings on magnetic resonance imaging (MRI) of the brain

MARC1 p.A165T variant is associated with decreased markers of liver injury and enhanced antioxidant capacity in autoimmune hepatitis

The clinical picture of autoimmune hepatitis (AIH) varies markedly between patients, potentially due to genetic modifiers. The aim of this study was to evaluate genetic variants previously associated with fatty liver as potential modulators of the AIH phenotype. The study cohort comprised 313 non-transplanted adults with AIH. In all patients, the MARC1 (rs2642438), HSD17B13 (rs72613567), PNPLA3 (rs738409), TM6SF2 (rs58542926), and MBOAT7 (rs641738) variants were genotyped using TaqMan assays. Mitochondrial damage markers in serum were analyzed in relation to the MARC1 variant. Carriers of the protective MARC1 allele had lower ALT and AST (both P < 0.05). In patients treated for AIH for ≥ 6 months, MARC1 correlated with reduced AST, ALP, GGT (all P ≤ 0.01), and lower APRI (P = 0.02). Patients carrying the protective MARC1 genotype had higher total antioxidant activity (P < 0.01) and catalase levels (P = 0.02) in serum. The PNPLA3 risk variant was associated with higher MELD (P = 0.02) in treated patients, whereas MBOAT7 increased the odds for liver cancer (OR = 3.71). None of the variants modulated the risk of death or transplantation. In conclusion, the MARC1 polymorphism has protective effects in AIH. Genotyping of MARC1, PNPLA3, and MBOAT7 polymorphisms might help to stratify patients with AIH

TGF-β1 and TGF-β2 abundance in liver diseases of mice and men

TGF-β1 is a major player in chronic liver diseases promoting fibrogenesis and tumorigenesis through various mechanisms. The expression and function of TGF-β2 have not been investigated thoroughly in liver disease to date. In this paper, we provide evidence that TGF-β2 expression correlates with fibrogenesis and liver cancer development. Using quantitative realtime PCR and ELISA, we show that TGF-β2 mRNA expression and secretion increased in murine HSCs and hepatocytes over time in culture and were found in the human-derived HSC cell line LX-2. TGF-β2 stimulation of the LX-2 cells led to upregulation of the TGF-β receptors 1, 2, and 3, whereas TGF-β1 treatment did not alter or decrease their expression. In liver regeneration and fibrosis upon CCl4 challenge, the transient increase of TGF-β2 expression was accompanied by TGF-β1 and collagen expression. In bile duct ligation-induced fibrosis, TGF-β2 upregulation correlated with fibrotic markers and was more prominent than TGF-β1 expression. Accordingly, MDR2-KO mice showed significant TGF-β2 upregulation within 3 to 15 months but minor TGF-β1 expression changes. In 5 of 8 hepatocellular carcinoma (HCC)/hepatoblastoma cell lines, relatively high TGF-β2 expression and secretion were observed, with some cell lines even secreting more TGF-β2 than TGF-β1. TGF-β2 was also upregulated in tumors of TGFα/cMyc and DEN-treated mice. The analysis of publically available microarray data of 13 human HCC collectives revealed considerable upregulation of TGF-β2 as compared to normal liver. Our study demonstrates upregulation of TGF-β2 in liver disease and suggests TGF-β2 as a promising therapeutic target for tackling fibrosis and HCC