Variants in the UGT1A1 gene and the risk of pediatric nonalcoholic fatty liver disease

The Evaluation of the Genetic Variation Types of the Uridine Diphosphate Glucuronosyl Transferase 1A1 Gene by Next-Generation Sequencing and Their Effects on Bilirubin Levels in Obese Children

Background and Objectives: Obesity is a major nutritional problem with an increasing prevalence among children and adolescents. The uridine-diphosphate-glucuronosyl-transferase1A1 (UGT1A1) gene encodes the UDP-glucuronosyl transferase enzyme, converting the toxic form of bilirubin to a soluble, nontoxic form. There are yet to be studies on the evaluation of the UGT1A1 variant types detected by next-generation sequencing (NGS) and their effects on bilirubin levels in nonsyndromic obese children. Methods: Forty-five children with body mass index (BMI) >95 percentile (p) constituted the obesity group and fourteen healthy children with BMI <85p constituted the control group. Anthropometric, clinical features, and biochemical parameters were evaluated. Furthermore, the UGT1A1 gene was sequenced by NGS. Results: The obese patients had lower total, direct, and indirect bilirubin levels (p = 0.422, 0.026, and 0.568, respectively). In addition, obese patients had more genetic variations in the UGT1A1 gene compared with the control group (62.2% and 50%, respectively). We found that children with variations had higher total direct and indirect bilirubin levels compared with those without variation (p = 0.016, 0.028, and 0.015, respectively). Children diagnosed with obesity in the first two years of their life had fewer genetic variations and lower total bilirubin levels (p = 0.000 and 0.013, respectively). Conclusions: It is assumed that bilirubin can be protective against many chronic diseases. Although bilirubin levels are found to be lower in obese children compared with the control group, some variations in the UGT1A1 gene may be supported by raising bilirubin. We suggest that high bilirubin levels caused by those UGT1A1 variations may be protective against obesity and its many negative effects.

Assessing the causal relationships between human blood metabolites and the risk of NAFLD: A comprehensive mendelian randomization study

Background: Non-alcoholic fatty liver disease (NAFLD) is a liver disease associated with obesity, insulin resistance, type 2 diabetes mellitus (T2DM), and metabolic syndrome. The risk factors for NAFLD have not been identified. Metabolic dysfunction has been found to be an important factor in the pathogenesis and progression of NAFLD. However, the causal impact of blood metabolites on NAFLD is unclear.

Methods: We performed a two-sample Mendelian randomization (MR) study. A genome-wide association study (GWAS) with 7824 participants provided data on 486 human blood metabolites. Outcome information was obtained from a large-scale GWAS meta-analysis of NAFLD, which contained 8,434 cases and 770,180 controls of Europeans. The inverse variance weighted (IVW) model was chosen as the primary two-sample MR analysis approach, followed by sensitivity analyses such as the heterogeneity test, horizontal pleiotropy test, and leave-one-out analysis. In addition, we performed replication, meta-analysis, and metabolic pathway analysis. We further conducted colocalization analysis to deeply reflect the causality.

Results: After rigorous genetic variant selection, IVW, sensitivity analysis, replication, and meta-analysis, two known metabolites were identified as being associated with the development of NAFLD [biliverdin: OR = 1.45; 95% CI 1.20-1.75; p = 0.0001; myristoleate: OR = 0.57; 95% CI 0.39-0.83; p = 0.0030].

Conclusion: By combining genomics with metabolomics, our findings provide a new perspective on the underlying mechanisms of NAFLD and have important implications for the screening and prevention of NAFLD.

Molecular mechanisms of metabolic associated fatty liver disease (MAFLD): functional analysis of lipid metabolism pathways

The metabolic-associated fatty liver disease (MAFLD) is a condition of fat accumulation in the liver in combination with metabolic dysfunction in the form of overweight or obesity and insulin resistance. It is also associated with an increased cardiovascular disease risk, including hypertension and atherosclerosis. Hepatic lipid metabolism is regulated by a combination of the uptake and export of fatty acids, de novo lipogenesis, and fat utilization by β-oxidation. When the balance between these pathways is altered, hepatic lipid accumulation commences, and long-term activation of inflammatory and fibrotic pathways can progress to worsen the liver disease. This review discusses the details of the molecular mechanisms regulating hepatic lipids and the emerging therapies targeting these pathways as potential future treatments for MAFLD.

Oxidative Stress in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a challenging disease caused by multiple factors, which may partly explain why it still remains an orphan of adequate therapies. This review highlights the interaction between oxidative stress (OS) and disturbed lipid metabolism. Several reactive oxygen species generators, including those produced in the gastrointestinal tract, contribute to the lipotoxic hepatic (and extrahepatic) damage by fatty acids and a great variety of their biologically active metabolites in a “multiple parallel-hit model”. This leads to inflammation and fibrogenesis and contributes to NAFLD progression. The alterations of the oxidant/antioxidant balance affect also metabolism-related organelles, leading to lipid peroxidation, mitochondrial dysfunction, and endoplasmic reticulum stress. This OS-induced damage is at least partially counteracted by the physiological antioxidant response. Therefore, modulation of this defense system emerges as an interesting target to prevent NAFLD development and progression. For instance, probiotics, prebiotics, diet, and fecal microbiota transplantation represent new therapeutic approaches targeting the gut microbiota dysbiosis. The OS and its counter-regulation are under the influence of individual genetic and epigenetic factors as well. In the near future, precision medicine taking into consideration genetic or environmental epigenetic risk factors, coupled with new OS biomarkers, will likely assist in noninvasive diagnosis and monitoring of NAFLD progression and in further personalizing treatments.

Reactive Oxygen Species (ROS) and Antioxidants as Immunomodulators in Exercise: Implications for Heme Oxygenase and Bilirubin

Exercise is commonly prescribed as a lifestyle treatment for chronic metabolic diseases as it functions as an insulin sensitizer, cardio-protectant, and essential lifestyle tool for effective weight maintenance. Exercise boosts the production of reactive oxygen species (ROS) and subsequent transient oxidative damage, which also upregulates counterbalancing endogenous antioxidants to protect from ROS-induced damage and inflammation. Exercise elevates heme oxygenase-1 (HO-1) and biliverdin reductase A (BVRA) expression as built-in protective mechanisms, which produce the most potent antioxidant, bilirubin. Together, these mitigate inflammation and adiposity. Moderately raising plasma bilirubin protects in two ways: (1) via its antioxidant capacity to reduce ROS and inflammation, and (2) its newly defined function as a hormone that activates the nuclear receptor transcription factor PPARα. It is now understood that increasing plasma bilirubin can also drive metabolic adaptions, which improve deleterious outcomes of weight gain and obesity, such as inflammation, type II diabetes, and cardiovascular diseases. The main objective of this review is to describe the function of bilirubin as an antioxidant and metabolic hormone and how the HO-1-BVRA-bilirubin-PPARα axis influences inflammation, metabolic function and interacts with exercise to improve outcomes of weight management.

Relationship of circulating total bilirubin, UDP-glucuronosyltransferases 1A1 and the development of non-alcoholic fatty liver disease: a cross-sectional study

Background

This study aimed to investigate the correlation of circulating total bilirubin (TB) and UGT1A1 with NAFLD in Chinese Han population.

Methods

172 adults were enrolled from the Qingdao Municipal Hospital from May 2019 to October 2020. All individuals were examined with MRI-PDFF and divided into no steatosis, mild steatosis, moderate steatosis, and severe steatosis groups according to the MRI-PDFF values. The biochemical indexes and UGT1A1 were measured.

Results

There was no significant difference of circulating TB and UGT1A1 levels between NAFLD group and controls. In the moderate steatosis and severe steatosis groups, the circulating TB levels were higher than that in control group (all P < 0.05). In addition, circulating TB levels were weak positively associated with liver fat fraction in NAFLD patients (ρ = 0.205, P = 0.001). There was no significant correlation between circulating UGT1A1 levels with liver fat fraction in patients with NAFLD (ρ = 0.080, P = 0.179), but positively correlation was found in patients with severe steatosis (ρ = 0.305, P = 0.026).

Conclusions

The circulating TB levels were significant high in patients with moderate and severe steatosis. Circulating TB levels were weakly associated with liver fat fraction in patients with NAFLD, and the circulating UGT1A1 levels were positively correlated with liver fat fraction in NAFLD patients with severe steatosis.

Trial registration: ChiCTR, ChiCTR1900022744. Registered 24 April 2019 – Retrospectively registered, http://www.chictr.org.cn/edit.aspx?pid=38304&htm=4.

Association of Serum Bilirubin and Functional Variants of Heme Oxygenase 1 and Bilirubin UDP-Glucuronosyl Transferase Genes in Czech Adult Patients with Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disorder worldwide. The aim of our study was to assess the role of bilirubin, and the heme oxygenase 1 (HMOX1) and bilirubin UDP-glucuronosyl transferase (UGT1A1) promoter gene variants, which are involved in bilirubin homeostasis, in the NAFLD development in adult patients. The study was performed on 84 patients with NAFLD and 103 age/sex-matched controls. Routine biochemistry, inflammatory markers, adipokines, and the fibrosis/steatohepatitis stage were determined in the NAFLD patients. The (GT)n/(TA)n dinucleotide variations in HMOX1/UGT1A1 gene promoters, respectively, were analyzed by fragment analysis. Compared to controls, serum bilirubin concentrations in NAFLD patients tended to be decreased, while the prevalence of phenotypic Gilbert syndrome was significantly low. Genetic variations in HMOX1 and UGT1A1 gene promoters did not differ between NAFLD patients and controls, and no relationship was found in the NAFLD patients between these gene variants and any of the laboratory or histological parameters. In conclusion, metabolism of bilirubin is dysregulated in NAFLD patients, most likely due to increased oxidative stress, since frequencies of the major functional variants in the HMOX1 or UGT1A1 gene promoters did not have any effect on development of NAFLD in adult patients.

Bilirubin deficiency renders mice susceptible to hepatic steatosis in the absence of insulin resistance

Background & aims

Plasma concentrations of bilirubin, a product of heme catabolism formed by biliverdin reductase A (BVRA), inversely associate with the risk of metabolic diseases including hepatic steatosis and diabetes mellitus in humans. Bilirubin has antioxidant and anti-inflammatory activities and may also regulate insulin signaling and peroxisome proliferator-activated receptor alpha (PPARα) activity. However, a causal link between bilirubin and metabolic diseases remains to be established. Here, we used the global Bvra gene knockout (Bvra^–/–) mouse as a model of deficiency in bilirubin to assess its role in metabolic diseases.

Approach & results

We fed mice fat-rich diets to induce hepatic steatosis and insulin resistance. Bile pigments were measured by LC-MS/MS, and hepatic lipids by LC-MS/MS (non-targeted lipidomics), HPLC-UV and Oil-Red-O staining. Oxidative stress was evaluated measuring F₂-isoprostanes by GC-MS. Glucose metabolism and insulin sensitivity were verified by glucose and insulin tolerance tests, ex vivo and in vivo glucose uptake, and Western blotting for insulin signaling. Compared with wild type littermates, Bvra^–/– mice contained negligible bilirubin in plasma and liver, and they had comparable glucose metabolism and insulin sensitivity. However, Bvra^–/– mice exhibited an inflamed and fatty liver phenotype, accompanied by hepatic accumulation of oxidized triacylglycerols and F₂-isoprostanes, in association with depletion of α-tocopherol. α-Tocopherol supplementation reversed the hepatic phenotype and observed biochemical changes in Bvra^–/– mice.

Conclusions

Our data suggests that BVRA deficiency renders mice susceptible to oxidative stress-induced hepatic steatosis in the absence of insulin resistance.

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Low plasma levels of bilirubin associate with increased metabolic disease risk.

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A direct link between bilirubin and metabolic disease remains to be established.

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Global BVRA deficiency causes global bilirubin deficiency and a fatty, inflamed liver.

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This hepatic phenotype is linked to decreased vitamin E and increased lipid oxidation.

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Vitamin E supplements restore normal liver phenotype in BVRA deficiency.

The Protective Role of the Heme Catabolic Pathway in Hepatic Disorders

Significance: As the central metabolic organ, the liver is exposed to a variety of potentially cytotoxic, proinflammatory, profibrotic, and carcinogenic stimuli. To protect the organism from these deleterious effects, the liver has evolved a number of defense systems, which include antioxidant substrates and enzymes, anti-inflammatory tools, enzymatic biotransformation systems, and metabolic pathways. Recent Advances: One of the pivotal systems that evolved during phylogenesis was the heme catabolic pathway. Comprising the important enzymes heme oxygenase and biliverdin reductase, this complex pathway has a number of key functions including enzymatic activities, but also cell signaling, and DNA transcription. It further generates two important bile pigments, biliverdin and bilirubin, as well as the gaseous molecule carbon monoxide. These heme degradation products have potent antioxidant, immunosuppressive, and cytoprotective effects. Recent data suggest that the pathway participates in the regulation of metabolic and hormonal processes implicated in the pathogenesis of hepatic and other diseases. Critical Issues: This review discusses the impact of the heme catabolic pathway on major liver diseases, with particular focus on the involvement of cellular targeting and signaling in the pathogenesis of these conditions. Future Directions: To utilize the biological consequences of the heme catabolic pathway, several unique therapeutic strategies have been developed. Research indicates that pharmaceutical, nutraceutical, and lifestyle modifications positively affect the pathway, delivering potentially long-term clinical benefits. However, further well-designed studies are needed to confirm the clinical benefits of these approaches. Antioxid. Redox Signal. 35, 734-752.

Association of Serum Bilirubin Level with Metabolic Syndrome and Non-Alcoholic Fatty Liver Disease: A Cross-Sectional Study of 1672 Obese Children

As in adults, obesity also plays a central role in the development of metabolic syndrome (MS) in children. Non-alcoholic fatty liver disease (NAFLD) is considered a manifestation of MS. Not only MS but also NAFLD seem to be inversely associated with serum bilirubin concentrations, an important endogenous tissue protector when only mild elevated. The aim of the study was to evaluate the association between serum bilirubin levels and the prevalence of MS and NAFLD in Italian obese children and adolescents. A retrospective cross-sectional study was performed in 1672 patients aged from 5 to 18 years. Clinical and laboratory parameters were assessed. NAFLD was measured by liver ultrasonography. The study was approved by the Ethical Committee of the Istituto Auxologico Italiano (research project code 1C021_2020, acronym BILOB). MS was present in 24% and fatty liver (FL) in 38% of this population. Bilirubin was not associated with FL and MS as a whole, but it was inversely associated only with selected components of MS, i.e., large WC, high blood pressure and high triglycerides. Our data suggest that bilirubin is not protective against MS and NAFLD in the presence of severe obesity.

Bilirubin as a metabolic hormone: the physiological relevance of low levels

Recent research on bilirubin, a historically well-known waste product of heme catabolism, suggests an entirely new function as a metabolic hormone that drives gene transcription by nuclear receptors. Studies are now revealing that low plasma bilirubin levels, defined as "hypobilirubinemia," are a possible new pathology analogous to the other end of the spectrum of extreme hyperbilirubinemia seen in patients with jaundice and liver dysfunction. Hypobilirubinemia is most commonly seen in patients with metabolic dysfunction, which may lead to cardiovascular complications and possibly stroke. We address the clinical significance of low bilirubin levels. A better understanding of bilirubin's hormonal function may explain why hypobilirubinemia might be deleterious. We present mechanisms by which bilirubin may be protective at mildly elevated levels and research directions that could generate treatment possibilities for patients with hypobilirubinemia, such as targeting of pathways that regulate its production or turnover or the newly designed bilirubin nanoparticles. Our review here calls for a shift in the perspective of an old molecule that could benefit millions of patients with hypobilirubinemia.

A Gilbert syndrome-associated haplotype protects against fatty liver disease in humanized transgenic mice

UDP-glucuronosyltransferases 1 A (UGT1A) enzymes are capable of detoxifying a broad range of endo- and xenobiotic compounds, which contributes to antioxidative effects, modulation of inflammation and cytoprotection. In the presence of low-function genetic UGT1A variants fibrosis development is increased in various diseases. This study aimed to examine the role of common UGT1A polymorphisms in NASH. Therefore, htgUGT1A-WT mice and htgUGT1A-SNP mice (carrying a common human haplotype present in 10% of the white population) were fed a high-fat Paigen diet for 24 weeks. Serum aminotransferase activities, hepatic triglycerides, fibrosis development and UGT1A expression were assessed. Microscopic examination revealed higher hepatic fat deposition and a significant induction of UGT1A gene expression in htgUGT1A-WT mice. In agreement with these observations, lower serum aminotransferase activities and lower expression levels of fibrosis-related genes were measured in htgUGT1A-SNP mice. This was accompanied by reduced PPARα protein levels in htgUGT1A-WT but not in SNP mice. Our data demonstrate a protective effect of a UGT1A SNP haplotype, leading to milder hepatic steatosis and NASH. Higher PPARα protein levels in animals with impaired UGT1A activity are the likely result of reduced glucuronidation of ligands involved in PPARα-mediated fatty acid oxidation and may lead to the observed protection in htgUGT1A-SNP mice.

New Perspectives on Genetic Prediction for Pediatric Metabolic Associated Fatty Liver Disease

Non-alcoholic or recently re-defined metabolic associated fatty liver disease (MAFLD), a spectrum of progressive hepatic disease, has become a public health issue in obese children and adolescents. MAFLD is a complex metabolic disease strongly associated with obesity and insulin resistance. It is not known why not every obese subject will develop MAFLD. Different ethnic/racial groups display differences in MAFLD prevalence, indicating genetic factor plays a role. In the past two decades, sequence variations in genetic loci, including PNPLA3, TM6SF2, GCKR, MBOAT7, HSD17B13, etc. have been shown to confer susceptibility to MAFLD in children and adults. This review article provides an updated viewpoint of genetic predictors related to pediatric MAFLD. We discuss whether these susceptible genes can be clinically used for risk stratification and personalized care. Understanding human genetics and molecular mechanisms can give important information not only for prediction of risk but also on how to design drugs. In view of current epidemic of MAFLD worldwide, it is necessary to identify which children with MAFLD progress rapidly and need earlier intervention. In the future, a comprehensive analysis of individualized genetic and environmental factors may help assess the risk of children with MAFLD and personalize their treatment.

Circulating total bilirubin and risk of non-alcoholic fatty liver disease in the PREVEND study: observational findings and a Mendelian randomization study

The relationship between circulating total bilirubin and incident non-alcoholic fatty liver disease (NAFLD) is uncertain. We aimed to assess the association of total bilirubin with the risk of new-onset NAFLD and investigate any causal relevance to the association using a Mendelian randomization (MR) study. Plasma total bilirubin levels were measured at baseline in the PREVEND prospective study of 3824 participants (aged 28–75 years) without pre-existing cardiovascular disease or NAFLD. Incident NAFLD was estimated using the biomarker-based algorithms, fatty liver index (FLI) and hepatic steatosis index (HSI). Odds ratios (ORs) (95% confidence intervals) for NAFLD were assessed. The genetic variant rs6742078 located in the UDP-glucuronosyltransferase (UGT1A1) locus was used as an instrumental variable. Participants were followed up for a mean duration of 4.2 years. The multivariable adjusted OR (95% CIs) for NAFLD as estimated by FLI (434 cases) was 0.82 (0.73–0.92; p = 0.001) per 1 standard deviation (SD) change in log_e total bilirubin. The corresponding adjusted OR (95% CIs) for NAFLD as estimated by HSI (452 cases) was 0.87 (0.78–0.97; p = 0.012). The rs6742078 variant explained 20% of bilirubin variation. The ORs (95% CIs) for a 1 SD genetically elevated total bilirubin level was 0.98 (0.69–1.38; p = 0.900) for FLI and 1.14 (0.81–1.59; p = 0.451) for HSI. Elevated levels of total bilirubin were not causally associated with decreased risk of NAFLD based on MR analysis. The observational association may be driven by biases such as unmeasured confounding and/or reverse causation. However, due to low statistical power, larger-scale investigations are necessary to draw definitive conclusions.

CRISPR Cas9-mediated deletion of biliverdin reductase A (BVRA) in mouse liver cells induces oxidative stress and lipid accumulation

Obesity is the predominant cause of non-alcoholic fatty liver disease (NAFLD), which is associated with insulin resistance and diabetes. NAFLD includes a spectrum of pathologies that starts with simple steatosis, which can progress to non-alcoholic steatohepatitis (NASH) with the commission of other factors such as the enhancement of reactive oxygen species (ROS). Biliverdin reductase A (BVRA) reduces biliverdin to the antioxidant bilirubin, which may serve to prevent NAFLD, and possibly the progression to NASH. To further understand the role of BVRA in hepatic function, we used CRISPR-Cas9 technology to target the Blvra gene in the murine hepa1c1c7 hepatocyte cell line (BVRA KO). BVRA activity and protein levels were significantly lower in BVRA KO vs. wild-type (WT) hepatocytes. Lipid accumulation under basal and serum-starved conditions was significantly (p < 0.05) higher in BVRA KO vs. WT cells. The loss of BVRA resulted in the reduction of mitochondria number, decreased expression of markers of mitochondrial biogenesis, uncoupling, oxidation, and fusion, which paralleled reduced mitochondrial oxygen consumption. BVRA KO cells exhibited increased levels of ROS generation and decreased levels of superoxide dismutase mRNA expression. In conclusion, our data demonstrate a critical role for BVRA in protecting against lipid accumulation and oxidative stress in hepatocytes, which may serve as a future therapeutic target for NAFLD and its progression to NASH.

Non-alcoholic fatty liver infiltration in children: an underdiagnosed evolving disease

Non-alcoholic fatty liver disease (NAFLD) constitutes the most common liver disease, one that is still underdiagnosed in pediatric populations (as well as in the general population), this due to the progressive increase in childhood obesity observed both in developed and developing countries during the last few decades. The pathophysiology of the disease has not been thoroughly clarified yet. The condition displays common pathways in adults and children; however, there are age-related differences. Unlike adults, children with NAFLD require extensive laboratory analysis, because underlying pathologies other than obesity may contribute to the evolution of the disease. Despite the presence of several serum markers and imaging techniques that contribute to NAFLD diagnosis, liver biopsy remains the gold standard diagnostic procedure. Early intervention and obesity prevention are mandatory, as NAFLD is reversible at an early stage. If left undiagnosed and untreated, NAFLD can progress to steatohepatitis (NASH) and subsequent liver failure, a potentially lethal complication. Of note, there are no treatment options when advanced liver fibrosis occurs. This review summarizes literature data on NAFLD in childhood indicating that this is an evolving disease and a significant component of the metabolic syndrome. Pediatricians should be aware of this entity, screening children at high risk and providing appropriate early management, in collaboration with pediatric subspecialists.

Genetically Regulated Bilirubin and Risk of Non-alcoholic Fatty Liver Disease: A Mendelian Randomization Study

Mildly elevated serum bilirubin levels were reported to be associated with decreased risk of non-alcoholic fatty liver disease (NAFLD). Whether this is a causal relationship remains unclear. We tested the hypothesis that genetically elevated plasma bilirubin levels are causally related to reduce risk of NAFLD. A total of 403 eligible participants were enrolled. NAFLD was determined by liver ultrasonography. The uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) gene variants (UGT1A1^*6 and UGT1A1^*28) were genotyped through sequencing. We applied a Mendelian randomization approach to assess the effects of genetically elevated bilirubin levels on NAFLD. NAFLD was diagnosed in 19% of participants in our study (NAFLD = 76; Non-NAFLD = 327). The variants of UGT1A1^*28 and UGT1A1^*6 were strongly associated with increased total bilirubin (TB), direct bilirubin (DB), and indirect bilirubin (IB) levels (each P < 0.001). These two common variants explain 12.7% (TB), 11.4% (IB), and 10.2% (DB) of the variance in bilirubin levels, respectively. In logistic regression model, after multifactorial adjustment for sex, age, aminotransferase (ALT), white blood count (WBC), and body mass index (BMI), variant UGT1A1^*28 (OR = 1.39; 95%CI: 0.614–3.170; P = 0.43) and UGT1A1^*6 (OR = 1.64, 95%CI, 0.78–3.44; P = 0.19) genotypes were not significantly associated with the risk of NAFLD. Moreover, the plasma bilirubin level (TB, IB, and DB) were not significantly associated with the risk of NAFLD (P > 0.30). A Mendelian randomization analysis of the UGT1A1 variants suggests that bilirubin is unlikely causally related with the risk of NAFLD.

Genetic determinants of hepatic steatosis and serum cytokeratin-18 fragment levels in Taiwanese children

BACKGROUND/AIMS

There are substantial genetic components contributing to the susceptibility of nonalcoholic fatty liver disease (NAFLD). It has recently been reported that the rs641738 C>T variant in the membrane-bound O-acyltransferase domain-containing protein 7 (MBOAT7) gene increased severity of NAFLD in adults of European descent. We aimed to test the hypothesis that MBOAT7 rs641738 variant would increase hepatic steatosis and hepatocellular injury in obese children.

METHODS

A total of 831 obese children aged 7-15 years were recruited. Hepatic steatosis was measured by ultrasonography. Because PNPLA3 rs738409, GCKR rs780094 and TM6SF2 rs58542926 variants are known to confer susceptibility to NAFLD, we assessed the influence of MBOAT7 rs641738 on hepatic steatosis, and serum levels of CK-18 fragment (a biomarker of hepatocellular injury and apoptosis for NAFLD) after adjusting the effects of PNPLA3, GCKR and TM6SF2 polymorphisms.

RESULTS

Of the recruited obese children, 22.7% had hepatic steatosis. PNPLA3 rs738409, GCKR rs780094 and TM6SF2 rs58542926 variants were independent risk factors of hepatic steatosis and elevated ALT levels. In contrast, MBOAT7 rs641738 variants, neither heterozygous nor homozygous genotypes, were not associated with hepatic steatosis, insulin resistance, lipid levels and liver enzymes. The multiple linear regression model revealed that after adjusting for age, gender, body mass index z score, PNPLA3 rs738409 and GCKR rs780094 variants, but not MBOAT7 rs641738, were associated with serum levels of CK-18 fragment.

CONCLUSIONS

The variant MBOAT7 rs641738 genotype is not associated with hepatic steatosis and serum levels of CK-18 fragment in obese Taiwanese children.

Bilirubin, a new therapeutic for kidney transplant?

In patients with end-stage renal disease, kidney transplantation has been associated with numerous benefits, including increased daily activity, and better survival rates. However, over 20% of kidney transplants result in rejection within five years. Rejection is primarily due to a hypersensitive immune system and ischemia/reperfusion injury. Bilirubin has been shown to be a potent antioxidant that is capable of potentially reversing or preventing damage from reactive oxygen species generated from ischemia and reperfusion. Additionally, bilirubin has several immunomodulatory effects that can dampen the immune system to promote organ acceptance. Increased bilirubin has also been shown to have a positive impact on renal hemodynamics, which is critical post-transplantation. Lastly, bilirubin levels have been correlated with biomarkers of successful transplantation. In this review, we discuss a multitude of potentially beneficial effects that bilirubin has on kidney acceptance of transplantation based on numerous clinical trials and animal models. Exogenous bilirubin delivery or increasing endogenous levels pre- or post-transplantation may have therapeutic benefits.

Biliverdin reductase and bilirubin in hepatic disease

The buildup of fat in the liver (hepatic steatosis) is the first step in a series of incidents that may drive hepatic disease. Obesity is the leading cause of nonalcoholic fatty liver disease (NAFLD), in which hepatic steatosis progresses to liver disease. Chronic alcohol exposure also induces fat accumulation in the liver and shares numerous similarities to obesity-induced NAFLD. Regardless of whether hepatic steatosis is due to obesity or long-term alcohol use, it still may lead to hepatic fibrosis, cirrhosis, or possibly hepatocellular carcinoma. The antioxidant bilirubin and the enzyme that generates it, biliverdin reductase A (BVRA), are components of the heme catabolic pathway that have been shown to reduce hepatic steatosis. This review discusses the roles for bilirubin and BVRA in the prevention of steatosis, their functions in the later stages of liver disease, and their potential therapeutic application.

Loss of biliverdin reductase-A promotes lipid accumulation and lipotoxicity in mouse proximal tubule cells

Obesity and increased lipid availability have been implicated in the development and progression of chronic kidney disease. One of the major sites of renal lipid accumulation is in the proximal tubule cells of the kidney, suggesting that these cells may be susceptible to lipotoxicity. We previously demonstrated that loss of hepatic biliverdin reductase A (BVRA) causes fat accumulation in livers of mice on a high-fat diet. To determine the role of BVRA in mouse proximal tubule cells, we generated a CRISPR targeting BVRA for a knockout in mouse proximal tubule cells (BVRA KO). The BVRA KO cells had significantly less metabolic potential and mitochondrial respiration, which was exacerbated by treatment with palmitic acid, a saturated fatty acid. The BVRA KO cells also showed increased intracellular triglycerides which were associated with higher fatty acid uptake gene cluster of differentiation 36 as well as increased de novo lipogenesis as measured by higher neutral lipids. Additionally, neutrophil gelatinase-associated lipocalin 1 expression, annexin-V FITC staining, and lactate dehydrogenase assays all demonstrated that BVRA KO cells are more sensitive to palmitic acid-induced lipotoxicity than wild-type cells. Phosphorylation of BAD which plays a role in cell survival pathways, was significantly reduced in palmitic acid-treated BVRA KO cells. These data demonstrate the protective role of BVRA in proximal tubule cells against saturated fatty acid-induced lipotoxicity and suggest that activating BVRA could provide a benefit in protecting from obesity-induced kidney injury.

Bilirubin in the Liver-Gut Signaling Axis

Bilirubin is a component of the heme catabolic pathway that is essential for liver function and has been shown to reduce hepatic fat accumulation. High plasma bilirubin levels are reflective of liver disease due to an injurious effect on hepatocytes. In healthy liver, bilirubin is conjugated and excreted to the intestine and converted by microbes to urobilinoids, which are reduced to the predominant pigment in feces, stercobilin, or reabsorbed. The function of urobilinoids in the gut or their physiological relevance of reabsorption is not well understood. In this review, we discuss the relationship of hepatic bilirubin signaling to the intestinal microbiota and its regulation of the liver-gut axis, as well as its capacity to mediate these processes.

The Genetics of Pediatric Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease in children. Severe fibrosis and cirrhosis are potential consequences of pediatric NAFLD and can occur within a few years of diagnosis. Observations suggest that genetics may be a strong modifying factor in the presentation, severity, and natural history of the disease. There is increasing interest in determining at-risk populations based on genetics in the hope of finding genotypes that correlate to NAFLD phenotype. Ultimately, the hope is to be able to tailor therapeutics to genetic predispositions and decrease disease morbidity in children with NAFLD.

Oxidative Stress as a Critical Factor in Nonalcoholic Fatty Liver Disease Pathogenesis

SIGNIFICANCE

Nonalcoholic fatty liver disease (NAFLD), characterized by liver triacylglycerol build-up, has been growing in the global world in concert with the raised prevalence of cardiometabolic disorders, including obesity, diabetes, and hyperlipemia. Redox imbalance has been suggested to be highly relevant to NAFLD pathogenesis. Recent Advances: As a major health problem, NAFLD progresses to the more severe nonalcoholic steatohepatitis (NASH) condition and predisposes susceptible individuals to liver and cardiovascular disease. Although NAFLD represents the predominant cause of chronic liver disorders, the mechanisms of its development and progression remain incompletely understood, even if various scientific groups ascribed them to the occurrence of insulin resistance, dyslipidemia, inflammation, and apoptosis. Nevertheless, oxidative stress (OxS) more and more appears as the most important pathological event during NAFLD development and the hallmark between simple steatosis and NASH manifestation.

CRITICAL ISSUES

The purpose of this article is to summarize recent developments in the understanding of NAFLD, essentially focusing on OxS as a major pathogenetic mechanism. Various attempts to translate reactive oxygen species (ROS) scavenging by antioxidants into experimental and clinical studies have yielded mostly encouraging results.

FUTURE DIRECTIONS

Although augmented concentrations of ROS and faulty antioxidant defense have been associated to NAFLD and related complications, mechanisms of action and proofs of principle should be highlighted to support the causative role of OxS and to translate its concept into the clinic. Antioxid. Redox Signal. 26, 519-541.

Does bilirubin prevent hepatic steatosis through activation of the PPARα nuclear receptor?

Several large population studies have demonstrated a negative correlation between serum bilirubin levels and the development of obesity, hepatic steatosis, and cardiovascular disease. Despite the strong correlative data demonstrating the protective role of bilirubin, the mechanism by which bilirubin can protect against these pathologies remains unknown. Bilirubin has long been known as a powerful antioxidant and also has anti-inflammatory actions, each of which may contribute to the protection afforded by increased levels. We have recently described a novel function of bilirubin as a ligand for the peroxisome proliferator-activated receptor-alpha (PPARα), which we show specifically binds to the nuclear receptor. Bilirubin may function as a selective PPAR modulator (SPPARM) to control lipid accumulation and blood glucose. However, it is not known to what degree bilirubin activation of PPARα is responsible for the protection afforded to reduce hepatic steatosis. We hypothesize that bilirubin, acting as a novel SPPARM, increases hepatic fatty acid metabolism through a PPARα-dependent mechanism which reduces hepatic lipid accumulation and protects against hepatic steatosis and non-alcoholic fatty liver disease (NAFLD).

A Guide to Non-Alcoholic Fatty Liver Disease in Childhood and Adolescence

Non-Alcoholic Fatty Liver Disease (NAFLD) is now the most prevalent form of chronic liver disease, affecting 10%–20% of the general paediatric population. Within the next 10 years it is expected to become the leading cause of liver pathology, liver failure and indication for liver transplantation in childhood and adolescence in the Western world. While our understanding of the pathophysiological mechanisms underlying this disease remains limited, it is thought to be the hepatic manifestation of more widespread metabolic dysfunction and is strongly associated with a number of metabolic risk factors, including insulin resistance, dyslipidaemia, cardiovascular disease and, most significantly, obesity. Despite this, ”paediatric” NAFLD remains under-studied, under-recognised and, potentially, undermanaged. This article will explore and evaluate our current understanding of NAFLD in childhood and adolescence and how it differs from adult NAFLD, in terms of its epidemiology, pathophysiology, natural history, diagnosis and clinical management. Given the current absence of definitive radiological and histopathological diagnostic tests, maintenance of a high clinical suspicion by all members of the multidisciplinary team in primary and specialist care settings remains the most potent of diagnostic tools, enabling early diagnosis and appropriate therapeutic intervention.

Heme oxygenase-1 gene promoter polymorphism and the risk of pediatric nonalcoholic fatty liver disease

BACKGROUND AND OBJECTIVES

Oxidative stress and the insulin-resistant state are thought to be key components in the pathogenesis of pediatric nonalcoholic fatty liver disease (NAFLD). Heme oxygenase (HO) is important in the defense against oxidative stress. This study aimed to assess the association of HO-1 gene promoter polymorphism and insulin resistance with NAFLD among obese children.

METHODS

A total of 101 obese children aged 6-17 years were recruited. Anthropometric, serum biochemical variables and biomarkers for glucose and insulin metabolism were measured. We screened the allelic frequencies of (GT)n repeats in the HO-1 gene promoter among these obese children. NAFLD was determined through liver ultrasonography. Because the distribution of numbers of (GT)n repeats was bimodal, we divided the alleles into two classes: class S included shorter (27) repeats, and class L included longer (⩾27) repeats. We assessed the effects of the length of (GT)n repeats in HO-1 gene promoter on pediatric NAFLD.

RESULTS

Of the 101 obese subjects, 27 (26.7%) had NAFLD. The alanine aminotransferase level was higher in patients carrying L alleles (L/L and L/S) than patients with S alleles (S/S) (46.2±49.3 IU|(-1) versus 30.2±20.1 IU|(-1); P=0.027). The significant risk factors for pediatric NAFLD were patients carrying L alleles (L/L and L/S) (odds ratio (OR)=18.84; 95% confidence interval (CI): 1.45-245.22; P=0.025), homeostasis model assessment of insulin resistance (OR=1.40; 95% CI: 1.07-1.83; P=0.014) and age (OR=1.24; 95% CI: 1.03-1.50; P=0.025).

CONCLUSION

In this hospital-based study, the obese children with longer GT repeats in the HO-1 gene promoter and insulin resistance were susceptible to NAFLD.

Nonalcoholic Fatty liver disease/non-alcoholic steatohepatitis in childhood: endocrine-metabolic "mal-programming"

CONTEXT

Nonalcoholic Fatty Liver Disease (NAFLD) is the major chronic liver disease in the pediatric population. NAFLD includes a broad spectrum of abnormalities (inflammation, fibrosis and cirrhosis), ranging from accumulation of fat (also known as steatosis) towards non-alcoholic steatohepatitis (NASH). The development of NAFLD in children is significantly increased.

EVIDENCE ACQUISITION

A literature search of electronic databases was undertaken for the major studies published from 1998 to today. The databases searched were: PubMed, EMBASE, Orphanet, Midline and Cochrane Library. We used the key words: "non-alcoholic fatty liver disease, children, non-alcoholic steatohepatitis and fatty liver".

RESULTS

NAFLD/NASH is probably promoted by "multiple parallel hits": environmental and genetic factors, systemic immunological disorders (oxidative stress, persistent-low grade of inflammation) as well as obesity and metabolic alterations (insulin resistance and metabolic syndrome). However its exact cause still underdiagnosed and unknown.

CONCLUSIONS

Pediatric NAFLD/NASH is emerging problem. Longitudinal follow-up studies, unfortunately still insufficient, are needed to better understand the natural history and outcome of NAFLD in children. This review focuses on the current knowledge regarding the epidemiology, pathogenesis, environmental, genetic and metabolic factors of disease. The review also highlights the importance of studying the underlying mechanisms of pediatric NAFLD and the need for complete and personalized approach in the management of NAFLD/NASH.

The association between indirect bilirubin levels and liver fibrosis due to chronic hepatitis C virus infection

We proposed to evaluate the association between serum indirect bilirubin levels and liver fibrosis in patients with chronic hepatitis C (CHC) genotype 1b. Biopsy proven CHC genotype 1b patients' demographics, clinical and histopathological characteristics were evaluated. Logistic regression analysis was done to evaluate the clinical, laboratory and demographic features of the histologically proven liver fibrosis in CHC patients. A total of 112 biopsy proven CHC genotype 1b patients were enrolled into the study. Liver fibrosis scores were measured by using Ishak fibrosis scores and were divided into two groups; fibrosis scores ≤ 2 were categorized as mild fibrosis, 82 patients (73.2%), whereas fibrosis scores >2 were categorized as advanced fibrosis group, 30 patients (26.8%). Patients with advanced fibrosis had lower indirect bilirubin levels than the mild fibrosis group (0.28 ± 0.02 mg/dl vs. 0.44 ± 0.032 mg/dl, p<0.001, respectively). Indirect bilirubin level was negatively correlated with advanced fibrosis scores (r=-0.416 and p<0.001). In multivariate logistic regression analysis, low indirect bilirubin level was an independent predicting factor of advanced liver fibrosis (OR: 0.001, 95% CI: 0.0-0.005, p<0.001). There is an inverse relationship between indirect bilirubin levels and advanced liver fibrosis caused by CHC genotype 1b.

Prevalence and risk factors for the development of nonalcoholic fatty liver disease in a nonobese Chinese population: the Zhejiang Zhenhai Study

OBJECTIVES

The precise prevalence and risk factors for the development of nonalcoholic fatty liver disease (NAFLD) in nonobese adults remains unclear. The objective of this study was to investigate the prevalence of NAFLD and risk factors for its development in a nonobese Chinese population.

METHODS

We firstly investigated the prevalence and factors associated with the presence of NAFLD in nonobese (body mass index (BMI) <25 kg/m(2)) Chinese subjects via a cross-sectional study, and then analyzed the risk factors for the development of NAFLD via a subsequent prospective 5-year follow-up of the same population.

RESULTS

A total of 6,905 nonobese subjects were enrolled in the cross-sectional study. Baseline evaluation revealed that the prevalence of NAFLD was 7.27%. A total of 5,562 subjects who were free of NAFLD at baseline completed the follow-up study, and 494 (8.88%) had developed NAFLD during the 5-year follow-up. Further analyses revealed that age, gender, BMI, waist circumference, triglyceride, high-density lipoprotein (HDL) cholesterol, serum uric acid, hemoglobin, and platelet count were independently associated with the presence and development of NAFLD.

CONCLUSIONS

NAFLD is prevalent in the nonobese Chinese population, and a substantial proportion of subjects developed NAFLD over the 5-year follow-up period. Special attention should be paid to the factors associated with the presence and development of NAFLD in nonobese subjects, to improve prevention and management of NAFLD.

Serum uric acid and non-alcoholic fatty liver disease in non-diabetic Chinese men

Increased serum uric acid (SUA) levels may be involved in the development of non-alcoholic fatty liver disease (NAFLD) in men presenting with metabolic syndrome (MetS) and/or insulin resistance. We aimed to determine the independent relationship between SUA and NAFLD in non-diabetic Chinese male population, and to explore the determinants of SUA levels among indexes of adiposity, lipid, and genotypes pertaining to triglycerides metabolism, inflammation, oxidative stress, and SUA concentrations. A total of 1440 men, classified depending on the presence of ultrasonographically detected NAFLD, underwent a complete healthy checkup program. Genotypes were extracted from our previously established genome-wide association study database. After adjusting for age, smoking, drinking, body mass index, homeostasis model assessment of insulin resistance, C-reactive protein, creatinine, alanine aminotransferase (ALT) and components of metabolic syndrome, the odds ratio for NAFLD, comparing the highest with the lowest SUA quartile, was 2.81 (95% confidence interval 1.66–4.76). A stepwise multivariate linear regression analysis (R² = 0.238, P<0.001) retained age, waist circumference, serum creatinine, triglycerides, the Q141K variant in ABCG2 (rs2231142) and NAFLD as significant predictors of SUA levels (all P<0.001). Besides, ALT and Met196Arg variant in TNFRSF1B (rs1061622) additionally associated with SUA among individuls with NAFLD. Our data suggest that in Chinese men, elevated SUA is significantly associated with NAFLD, independent of insulin resistance and other metabolic disorders, such as central obesity or hypertriglyceridemia. Meanwhile, among subjects with NAFLD, index of liver damage, such as elevated ALT combined with genetic susceptibility to inflammation associated with increased SUA levels.

Serum bilirubin level is inversely associated with nonalcoholic steatohepatitis in children

OBJECTIVES

Oxidative stress has been implicated in the development of nonalcoholic fatty liver disease (NAFLD) and progression to the more severe form, nonalcoholic steatohepatitis (NASH), in children. We aimed to study the clinical correlation between bilirubin, a potent endogenous antioxidant with cytoprotective properties, and histopathological findings in pediatric patients with NAFLD.

METHODS

We included consecutive children with biopsy-proven NAFLD and obtained demographic, clinical, and histopathological data. We performed logistic regression analysis to assess the clinical factors associated with the histological features of NASH or fibrosis.

RESULTS

From a total of 302 biopsies, 67% (203) had evidence of NASH, whereas 64.2% had some degree of fibrosis (stage 1 in 51%, stage 2 in 6.3%, and stage 3 in 6.6%). Mean total bilirubin was significantly lower in the NASH group compared with the non-NASH group (0.65 ± 0.24 vs 0.73 ± 0.22 mg/dL, P = 0.007). Higher total bilirubin levels were negatively correlated with the presence of steatosis and the NAFLD activity score (P < 0.05), whereas a trend in that direction was observed for presence of fibrosis and inflammation (P = 0.051). On multivariable analysis, higher bilirubin levels were significantly associated with a decreased likelihood of a histological diagnosis of NASH on biopsy (odds ratio 0.29, 95% CI 0.10-0.85, P = 0.024).

CONCLUSIONS

In children with NAFLD, there is an inverse relation between serum bilirubin levels and the presence of NASH on biopsy. This may be secondary to the antioxidant effect of bilirubin.

Genomic aspects of NAFLD pathogenesis

Non-alcoholic fatty liver disease (NAFLD) is the most predominant liver disease worldwide and hepatic manifestation of the metabolic syndrome. Its histology spectrum ranges from steatosis, to steatohepatitis (NASH) that can further progress to cirrhosis and hepatocellular carcinoma (HCC). The increasing incidence of NAFLD has contributed to rising numbers of HCC occurrences. NAFLD progression is governed by genetic susceptibility, environmental factors, lifestyle and features of the metabolic syndrome, many of which overlap with HCC. Gene expression profiling and genome wide association studies have identified novel disease pathways and polymorphisms in genes that may be potential biomarkers of NAFLD progression. However, the multifactorial nature of NAFLD and the limited number of sufficiently powered studies are among the current limitations for validated biomarkers of clinical utility. Further studies incorporating the links between circadian regulation and hepatic metabolism might represent an additional direction in the search for predictive biomarkers of liver disease progression and treatment outcomes.

A common variant in the peroxisome proliferator-activated receptor-γ coactivator-1α gene is associated with nonalcoholic fatty liver disease in obese children

BACKGROUND

The single nucleotide polymorphism in the peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α gene (PPARGC1A) was identified to be associated with nonalcoholic fatty liver disease (NAFLD) in adults. The PPARGC1A gene encodes PGC-1α, which regulates cellular energy metabolism.

OBJECTIVE

We aimed to test the hypothesis that the PPARGC1A rs8192678 risk A allele would influence the risk of NAFLD in obese children.

DESIGN

We genotyped PPARGC1A rs8192678 and PNPLA3 rs738409 in 781 obese children aged 7-18 y. NAFLD was determined by ultrasonography. We evaluated the independent influence of the PPARGC1A rs8192678 risk A allele on pediatric NAFLD after control for the effect of the PNPLA3 rs738409 polymorphism.

RESULTS

A total of 23.3% of the recruited obese children had NAFLD. PNPLA3 rs738409 increased the OR of NAFLD by 1.622 (95% CI: 1.071, 2.457; P = 0.023) in subjects with GC alleles and 2.659 (95% CI: 1.509, 4.686; P < 0.001) for GG alleles, as compared with CC alleles. After control for the effects of age- and sex-adjusted BMI, sex, and PNPLA3 rs738409 polymorphism, the PPARGC1A rs8192678 risk A allele was an independent risk factor for developing NAFLD, with an OR of 1.740 (95% CI: 1.149, 2.637; P = 0.009). Subjects with the PPARGC1A rs8192678 risk A allele had an increase in the mean serum alanine aminotransferase concentration of 5.2 IU/L, as compared with subjects without this allele (P = 0.011).

CONCLUSION

The PPARGC1A rs8192678 risk A allele is associated with an increased risk of NAFLD, independent of the effect of the PNPLA3 rs738409 polymorphism in our population of obese Taiwanese children.

Molecular Interactions between NAFLD and Xenobiotic Metabolism

Non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, is a complex multifactorial disease characterized by metabolic deregulations that include accumulation of lipids in the liver, lipotoxicity, and insulin resistance. The progression of NAFLD to non-alcoholic steatohepatitis and cirrhosis, and ultimately to carcinomas, is governed by interplay of pro-inflammatory pathways, oxidative stress, as well as fibrogenic and apoptotic cues. As the liver is the major organ of biotransformation, deregulations in hepatic signaling pathways have effects on both, xenobiotic and endobiotic metabolism. Several major nuclear receptors involved in the transcription and regulation of phase I and II drug metabolizing enzymes and transporters also have endobiotic ligands including several lipids. Hence, hepatic lipid accumulation in steatosis and NAFLD, which leads to deregulated activation patterns of nuclear receptors, may result in altered drug metabolism capacity in NAFLD patients. On the other hand, genetic and association studies have indicated that a malfunction in drug metabolism can affect the prevalence and severity of NAFLD. This review focuses on the complex interplay between NAFLD pathogenesis and drug metabolism. A better understanding of these relationships is a prerequisite for developing improved drug dosing algorithms for the pharmacotherapy of patients with different stages of NAFLD.

Unconjugated hyperbilirubinemia is inversely associated with non-alcoholic steatohepatitis (NASH)

BACKGROUND

It has been recognised that unconjugated bilirubin contains hepatic anti-fibrogenic and anti-inflammatory properties and is a potent physiological antioxidant cytoprotectant. We believe that unconjugated hyperbilirubinemia may protect against development of non-alcoholic steatohepatitis (NASH).

AIM

This study was conducted to assess the association of serum unconjugated bilirubin levels and histological liver damage in non-alcoholic fatty liver disease (NAFLD).

METHODS

This was a retrospective analysis involving adult patients from a tertiary medical centre undergoing liver biopsy to evaluate suspected NAFLD or NASH and a control group without NAFLD based on normal liver ultrasound, labs and history. Identification of unconjugated hyperbilirubinemia was based on the presence of predominantly unconjugated bilirubin ≥1.0 mg/dL (17.1 μmol/L) while fasting, in the absence of haemolytic disease or other hepatic function alteration.

RESULTS

Six-hundred and forty-one patients were included. Unconjugated hyperbilirubinemia was inversely associated with NASH (OR 16.1, 95% CI 3.7-70.8 P < 0.001). Of the patients without NAFLD (133 patients), 13 (9.8%) had unconjugated hyperbilirubinemia (range 1.0-1.8, mean 1.4). Of the patients with NAFLD without NASH (285 patients), 32 (11.2%) had unconjugated hyperbilirubinemia (range 1.0-3.0, mean 1.4). Of the patients with NASH (223 patients), three (1.3%) had unconjugated hyperbilirubinemia (1.0, 1.1, 1.4).

CONCLUSIONS

Unconjugated hyperbilirubinemia is inversely associated with the histopathological severity of liver damage in non-alcoholic fatty liver disease.

A cohort study of serum bilirubin levels and incident non-alcoholic fatty liver disease in middle aged Korean workers

Background

Serum bilirubin may have potent antioxidant and cytoprotective effects. Serum bilirubin levels are inversely associated with several cardiovascular and metabolic endpoints, but their association with nonalcoholic fatty liver disease (NAFLD) has not been investigated except for a single cross-sectional study in a pediatric population. We assessed the prospective association between serum bilirubin concentrations (total, direct, and indirect) and the risk for NAFLD.

Methods and Findings

We performed a cohort study in 5,900 Korean men, 30 to 59 years of age, with no evidence of liver disease and no major risk factors for liver disease at baseline. Study participants were followed in annual or biennial health examinations between 2002 and 2009. The presence of fatty liver was determined at each visit by ultrasonography. We observed 1,938 incident cases of NAFLD during 28,101.8 person-years of follow-up. Increasing levels of serum direct bilirubin were progressively associated with a decreasing incidence of NAFLD. In age-adjusted models, the hazard ratio for NAFLD comparing the highest to the lowest quartile of serum direct bilirubin levels was 0.61 (95% CI 0.54–0.68). The association persisted after adjusting for multiple metabolic parameters (hazard ratio comparing the highest to the lowest quartile 0.86, 95% CI 0.76–0.98; P trend = 0.039). Neither serum total nor indirect bilirubin levels were significantly associated with the incidence of NAFLD.

Conclusions

In this large prospective study, higher serum direct bilirubin levels were significantly associated with a lower risk of developing NAFLD, even adjusting for a variety of metabolic parameters. Further research is needed to elucidate the mechanisms underlying this association and to establish the role of serum direct bilirubin as a marker for NAFLD risk.

Diagnosis of nonalcoholic fatty liver disease in children and adolescents: position paper of the ESPGHAN Hepatology Committee

Nonalcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in children and adolescents in the United States, and most probably also in the rest of the industrialized world.As the prevalence of NAFLD in childhood increases with the worldwide obesity epidemic, there is an urgent need for diagnostic standards that can be commonly used by pediatricians and hepatologists. To this end, we performed a PubMed search of the adult and pediatric literature on NAFLD diagnosis through May 2011 using Topics and/or relevant Authors as search words. According to the present literature, NAFLD is suspected based on the association of fatty liver combined with risk factors (mainly obesity), after the exclusion of other causes of liver disease. The reference but imperfect standard for confirming NAFLD is liver histology. The following surrogate markers are presently used to estimate degree of steatosis and liver fibrosis and risk of progression to end-stage liver disease: imaging by ultrasonography or magnetic resonance imaging, liver function tests, and serum markers of liver fibrosis.NAFLD should be suspected in all of the overweight or obese children and adolescents older than 3 years with increased waist circumference especially if there is a NAFLD history in relatives. The typical presentation, however, is in children ages 10 years and older. The first diagnostic step in these children should be abdominal ultrasound and liver function tests, followed by exclusion of other liver diseases. Overweight/obese children with normal ultrasonographic imaging and normal liver function tests should still be monitored due to the poor sensitivity of these tests at a single assessment.Indications for liver biopsy include the following: to rule out other treatable diseases, in cases of clinically suspected advanced liver disease, before pharmacological/surgical treatment, and as part of a structured intervention protocol or clinical research trial.

The role of bilirubin in diabetes, metabolic syndrome, and cardiovascular diseases

Bilirubin belongs to a phylogenetically old superfamily of tetrapyrrolic compounds, which have multiple biological functions. Although for decades bilirubin was believed to be only a waste product of the heme catabolic pathway at best, and a potentially toxic compound at worst; recent data has convincingly demonstrated that mildly elevated serum bilirubin levels are strongly associated with a lower prevalence of oxidative stress-mediated diseases. Indeed, serum bilirubin has been consistently shown to be negatively correlated to cardiovascular diseases (CVD), as well as to CVD-related diseases and risk factors such as arterial hypertension, diabetes mellitus, metabolic syndrome, and obesity. In addition, the clinical data are strongly supported by evidence arising from both in vitro and in vivo experimental studies. This data not only shows the protective effects of bilirubin per se; but additionally, of other products of the heme catabolic pathway such as biliverdin and carbon monoxide, as well as its key enzymes (heme oxygenase and biliverdin reductase); thus, further underlining the biological impacts of this pathway. In this review, detailed information on the experimental and clinical evidence between the heme catabolic pathway and CVD, and those related diseases such as diabetes, metabolic syndrome, and obesity is provided. All of these pathological conditions represent an important threat to human civilization, being the major killers in developed countries, with a steadily increasing prevalence. Thus, it is extremely important to search for novel markers of these diseases, as well as for novel therapeutic modalities to reverse this unfavorable situation. The heme catabolic pathway seems to fulfill the criteria for both diagnostic purposes as well as for potential therapeutical interventions.

Unconjugated hyperbilirubinemia in patients with non-alcoholic fatty liver disease: a favorable endogenous response

The clinical significance of increased frequency of unconjugated hyperbilirubinemia in patients with non-alcoholic fatty liver disease (NAFLD) is unknown. Serum bilirubin is an endogenous anti-oxidant, and oxidative stress plays an important role in the pathogenesis of NAFLD. In this study, we have documented 25.4% prevalence of unconjugated hyperbilirubinemia in 204 consecutive NAFLD patients. These patients had a significantly less severe liver disease on histopathology and/or fibroScan which may be attributed to anti-oxidant effect of bilirubin.

Pediatric nonalcoholic fatty liver disease: a multidisciplinary approach

Nonalcoholic fatty liver disease (NAFLD) is a multifactorial condition, ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) with or without fibrosis. NAFLD affects both adults and children who present with particular risk factors, including obesity, sedentary lifestyle and/or a predisposing genetic background. The escalation of the prevalence of NAFLD in children worldwide is a worrying phenomenon because this disease is closely associated with the development of both cirrhosis and cardiometabolic syndrome in adulthood. The etiopathogenesis of primary NAFLD in children is unknown; however, considerable knowledge about the mechanisms of liver damage that occur during disease progression has been gathered over the past 30 years. Understanding the pathogenetic mechanisms, together with the histological pattern, provide the basis to characterize potential early predictors of the disease, suitable noninvasive diagnostic tools and design novel specific treatments and possible management strategies. Despite a few clinical trials on the use of antioxidants combined with lifestyle intervention for NAFLD that showed encouraging results, to date, no treatment guidelines exist for children with NAFLD. In this Review, we provide an overview of current concepts in epidemiology, histological features, etiopathogenesis, diagnosis and treatment of NAFLD in children and adolescents.

DetoxiProt: an integrated database for detoxification proteins

Background

Detoxification proteins are a class of proteins for degradation and/or elimination of endogenous and exogenous toxins or medicines, as well as reactive oxygen species (ROS) produced by these materials. Most of these proteins are generated as a response to the stimulation of toxins or medicines. They are essential for the clearance of harmful substances and for maintenance of physiological balance in organisms. Thus, it is important to collect and integrate information on detoxification proteins.

Results

To store, retrieve and analyze the information related to their features and functions, we developed the DetoxiProt, a comprehensive database for annotation of these proteins. This database provides detailed introductions about different classes of the detoxification proteins. Extensive annotations of these proteins, including sequences, structures, features, inducers, inhibitors, substrates, chromosomal location, functional domains as well as physiological-biochemical properties were generated. Furthermore, pre-computed BLAST results, multiple sequence alignments and evolutionary trees for detoxification proteins are also provided for evolutionary study of conserved function and pathways. The current version of DetoxiProt contains 5956 protein entries distributed in 628 organisms. An easy to use web interface was designed, so that annotations about each detoxification protein can be retrieved by browsing with a specific method or by searching with different criteria.

Conclusions

DetoxiProt provides an effective and efficient way of accessing the detoxification protein sequences and other high-quality information. This database would be a valuable source for toxicologists, pharmacologists and medicinal chemists. DetoxiProt database is freely available at http://lifecenter.sgst.cn/detoxiprot/.

Genetic factors associated with the presence and progression of nonalcoholic fatty liver disease: a narrative review

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world. Whereas insulin resistance and obesity are considered major risk factors for the development and progression of NAFLD, the genetic underpinnings are unclear. Before 2008, candidate gene studies based on prior knowledge of pathophysiology of fatty liver yielded conflicting results. In 2008, Romeo et al. published the first genome wide association study and reported the strongest genetic signal for the presence of fatty liver (PNPLA3, patatin-like phospholipase domain containing 3; rs738409). Since then, two additional genome wide scans were published and identified 9 additional genetic variants. Whereas these results shed light into the understanding of the genetics of NAFLD, most of associations have not been replicated in independent samples and, therefore, remain undetermined the significance of these findings. This review aims to summarize the understanding of genetic epidemiology of NAFLD and highlights the gaps in knowledge.

GWAS of butyrylcholinesterase activity identifies four novel loci, independent effects within BCHE and secondary associations with metabolic risk factors

Serum butyrylcholinesterase (BCHE) activity is associated with obesity, blood pressure and biomarkers of cardiovascular and diabetes risk. We have conducted a genome-wide association scan to discover genetic variants affecting BCHE activity, and to clarify whether the associations between BCHE activity and cardiometabolic risk factors are caused by variation in BCHE or whether BCHE variation is secondary to the metabolic abnormalities. We measured serum BCHE in adolescents and adults from three cohorts of Australian twin and family studies. The genotypes from ∼2.4 million single-nucleotide polymorphisms (SNPs) were available in 8791 participants with BCHE measurements. We detected significant associations with BCHE activity at three independent groups of SNPs at the BCHE locus (P = 5.8 × 10(-262), 7.8 × 10(-47), 2.9 × 10(-12)) and at four other loci: RNPEP (P = 9.4 × 10(-16)), RAPH1-ABI2 (P = 4.1 × 10(-18)), UGT1A1 (P = 4.0 × 10(-8)) and an intergenic region on chromosome 8 (P = 1.4 × 10(-8)). These loci affecting BCHE activity were not associated with metabolic risk factors. On the other hand, SNPs in genes previously associated with metabolic risk had effects on BCHE activity more often than can be explained by chance. In particular, SNPs within FTO and GCKR were associated with BCHE activity, but their effects were partly mediated by body mass index and triglycerides, respectively. We conclude that variation in BCHE activity is due to multiple variants across the spectrum from uncommon/large effect to common/small effect, and partly results from (rather than causes) metabolic abnormalities.

A common variant in the PNPLA3 gene is a risk factor for non-alcoholic fatty liver disease in obese Taiwanese children

OBJECTIVE

To test the hypothesis that the presence of the PNPLA3 rs738409 G allele would increase the susceptibility of non-alcoholic fatty liver disease (NAFLD) in obese Taiwanese children.

STUDY DESIGN

A total of 520 obese children aged 6-18 years were recruited. Their PNPLA3 rs738409 genotypes-CC, CG, or GG-were detected by the 5'-nuclease assay. The effects of the PNPLA3 rs738409 G allele on pediatric NAFLD were evaluated based on liver ultrasonography findings and mean serum alanine aminotransferase levels in these children.

RESULTS

NAFLD was present in 19.6% of the obese children. In comparison to the subjects with CC alleles, the risk of NAFLD was increased by 2.96-fold (95% CI, 1.57 to 5.59, P = .0008) in the subjects with CG alleles and by 5.84-fold (95% CI, 2.59 to 13.16; P < .0001) in those with GG alleles. Variant PNPLA3 rs738409 genotypes were associated with increases in mean serum alanine aminotransferase level of 4.77 IU/L (P = .0435) in subjects with CG alleles and of 10.86 IU/L (P < .0001) in those with GG alleles compared with subjects with CC alleles.

CONCLUSIONS

The variant PNPLA3 rs738409 genotypes increased the risk of NAFLD in our population of obese Taiwanese children. The effect of the G allele on pediatric NAFLD followed a dominant genetic model.

Genetic determinants of susceptibility and severity in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) in most patients involves only simple hepatic steatosis; however, a minority develop progressive steatohepatitis. Family studies and inter-ethnic differences in susceptibility suggest that genetic factors may be important risk determinants for progressive disease. Polymorphisms in genes affecting lipid metabolism, cytokines, fibrotic mediators and oxidative stress may be associated with steatohepatitis and/or fibrosis, but most of these findings require replication. A recent finding that a nonsynonymous polymorphism in the PNPLA3 gene predicts the extent of steatosis in NAFLD has been replicated in at least eight studies, with several studies also demonstrating an association with fibrosis. A new genome-wide association study has identified several additional novel associations with NAFLD severity. Other disease genes may be identified by similar approaches in the future.

Genetic determinants of hepatic steatosis in man

Hepatic steatosis is one of the most common liver disorders in the general population. The main cause of hepatic steatosis is nonalcoholic fatty liver disease (NAFLD), representing the hepatic component of the metabolic syndrome, which is characterized by type 2 diabetes, obesity, and dyslipidemia. Insulin resistance and excess adiposity are considered to play key roles in the pathogenesis of NAFLD. Although the risk factors for NAFLD are well established, the genetic basis of hepatic steatosis is largely unknown. Here we review recent progress on genomic variants and their association with hepatic steatosis and discuss the potential impact of these genetic studies on clinical practice. Identifying the genetic determinants of hepatic steatosis will lead to a better understanding of the pathogenesis and progression of NAFLD.

Nonalcoholic fatty liver in Asia: Firmly entrenched and rapidly gaining ground

Nonalcoholic fatty liver disease (NAFLD) is becoming an important chronic liver disorder in Asia. Prevalence figures show regional variations but at least 10% of the general population in Asia have fatty liver. Fatty liver can develop with relatively small changes in weight (2-3 kg), often with increasing central adiposity. The metabolic syndrome may precede or follow NAFLD. Overt diabetes is present in one-third of cases but when oral glucose tolerance tests are performed, a further third of individuals have impaired glucose tolerance or diabetes. Natural history data are still scarce but cases of advanced hepatic fibrosis and hepatocellular carcinoma are now regularly reported. Many cases of cryptogenic cirrhosis are also attributable to NAFLD. Histological progression has been demonstrated for patients with NASH as well as for those with hepatic steatosis alone. Genetic factors may in part contribute to the rise in NAFLD. Polymorphisms within apolipoprotein C3 (APOC3) gene have been linked to NAFLD in lean Indian men. Although a number of other polymorphisms involving genes controlling adipose distribution, insulin signalling, adipokine responses and hepatic fibrosis have been reported, these studies have been underpowered. Transient elastography could help in detecting and monitoring hepatic fibrosis but further refinements in technique are necessary for obese individuals. Of the biomarkers, hyaluronic acid and cytokeratin-18 fragment testing show promise as markers of hepatic fibrosis and NASH, respectively. Lifestyle alterations including dietary changes and increased physical activity remain the cornerstone of management. Attention should be paid to prevention through public education of campaigns addressing the increase in both adult and childhood obesity.

Update on nonalcoholic fatty liver disease: genes involved in nonalcoholic fatty liver disease and associated inflammation

PURPOSE OF REVIEW

Nonalcoholic fatty liver disease (NAFLD) is one of the most prevalent liver diseases worldwide. Advanced age, extensive overweight and a number of features of the metabolic syndrome are associated with NAFLD severity. The cause of NAFLD is considered multifactorial with a substantial genetic component.

RECENT FINDINGS

Family members of children with NAFLD demonstrate a higher risk for NAFLD. Whereas such an association only suggests that familial factors are major determinants of whether or not an individual will develop NAFLD, recent genome-wide association studies were able to identify first candidate genes. An allele in patatin-like phospholipase 3, encoding a protein of unknown function with homology to lipid acyl hydrolases, is strongly associated with increased hepatic fat and inflammation. Apolipoprotein C3 gene variants are also associated with NAFLD and insulin resistance. Several other genetic variants have been identified, although with less convincing evidence. These genetic variants involve molecules regulating insulin signaling, lipid metabolism, oxidative stress or fibrogenesis. Furthermore, genetic variants of several cytokines and adipocytokines have been associated with NAFLD.

SUMMARY

Several genetic factors such as patatin-like phospholipase 3 or apolipoprotein C3 have been recently characterized in NAFLD. Further studies to identify their interaction with environmental factors are eagerly warranted.