Ariel E. Feldstein

Gut flora metabolism of phosphatidylcholine promotes cardiovascular disease

Metabolomics studies hold promise for the discovery of pathways linked to disease processes. Cardiovascular disease (CVD) represents the leading cause of death and morbidity worldwide. Here we used a metabolomics approach to generate unbiased small-molecule metabolic profiles in plasma that predict risk for CVD. Three metabolites of the dietary lipid phosphatidylcholine—choline, trimethylamine N-oxide (TMAO) and betaine—were identified and then shown to predict risk for CVD in an independent large clinical cohort. Dietary supplementation of mice with choline, TMAO or betaine promoted upregulation of multiple macrophage scavenger receptors linked to atherosclerosis, and supplementation with choline or TMAO promoted atherosclerosis. Studies using germ-free mice confirmed a critical role for dietary choline and gut flora in TMAO production, augmented macrophage cholesterol accumulation and foam cell formation. Suppression of intestinal microflora in atherosclerosis-prone mice inhibited dietary-choline-enhanced atherosclerosis. Genetic variations controlling expression of flavin monooxygenases, an enzymatic source of TMAO, segregated with atherosclerosis in hyperlipidaemic mice. Discovery of a relationship between gut-flora-dependent metabolism of dietary phosphatidylcholine and CVD pathogenesis provides opportunities for the development of new diagnostic tests and therapeutic approaches for atherosclerotic heart disease.

Hepatocyte apoptosis and fas expression are prominent features of human nonalcoholic steatohepatitis

BACKGROUND & AIMS The pathogenesis of nonalcoholic steatohepatitis (NASH) remains poorly understood. Although apoptosis is a common mechanism of liver injury, the extent and clinical significance of apoptosis in NASH has not been examined. Thus, the aims of this study were to quantify hepatocyte apoptosis in NASH, correlate it with disease severity, and identify possible mechanisms of apoptosis induction. METHODS Hepatocyte apoptosis was assessed in NASH, simple steatosis, alcoholic hepatitis, and controls without liver disease using the TUNEL assay and immunohistochemistry for activated caspases 3 and 7. Liver specimens were also graded according to the magnitude of inflammation and fibrosis. RESULTS TUNEL-positive cells were significantly increased in liver biopsy specimens from patients with NASH compared with simple steatosis and controls. Unexpectedly, TUNEL-positive cells were also greater in NASH vs. alcoholic hepatitis. Immunohistochemistry demonstrated active caspases 3 and 7 in NASH specimens, confirming the occurrence of apoptosis in this disease. A positive correlation was observed between hepatocyte apoptosis and hepatic fibrosis and inflammatory activity, respectively. The Fas receptor was strongly expressed in hepatocytes in liver specimens from NASH patients as compared with controls. CONCLUSIONS Hepatocyte apoptosis is significantly increased in patients with NASH and correlates with disease severity, suggesting that antiapoptotic therapy may be useful in this syndrome.

Free fatty acids promote hepatic lipotoxicity by stimulating TNF-α expression via a lysosomal pathway

Nonalcoholic fatty liver disease (NAFLD) is a serious health problem. Although NAFLD represents a form of lipotoxicity, its pathogenesis remains poorly understood. The aim of this study was to examine the cellular mechanisms involved in free fatty acid (FFA)‐mediated hepatic lipotoxicity. FFA treatment of liver cells resulted in Bax translocation to lysosomes and lysosomal destabilization with release of cathepsin B (ctsb), a lysosomal cysteine protease, into the cytosol. This process was also partially dependent on ctsb. Lysosomal destabilization resulted in nuclear factor κB–dependent tumor necrosis factor α expression. Release of ctsb into the cytoplasm was also observed in humans with NAFLD and correlated with disease severity. In a dietary murine model of NAFLD, either genetic or pharmacological inactivation of ctsb protected against development of hepatic steatosis, liver injury, and insulin resistance with its associated “dysmetabolic syndrome.” In conclusion, these data support a lipotoxic model of FFA‐mediated lysosomal destabilization. Supplemental material for this article can be found on the HEPATOLOGY website (http://www.interscience.wiley.com/jpages/0270‐9139/suppmat/index.html). (HEPATOLOGY 2004;40:185–194.)

In vivo assessment of liver cell apoptosis as a novel biomarker of disease severity in nonalcoholic fatty liver disease

In patients with nonalcoholic fatty liver disease (NAFLD), a liver biopsy remains the only reliable way to differentiate simple steatosis from nonalcoholic steatohepatitis (NASH). Noninvasive methods are urgently needed. Increasing evidence suggests hepatocyte apoptosis is a key mediator of liver injury in NAFLD. The aim of this study was to quantify hepatocyte apoptosis in plasma from patients with NAFLD and correlate it with histological severity. Plasma was obtained from 44 consecutive patients with suspected NAFLD at the time of liver biopsy. Histology was assessed blindly. Caspase‐3–generated cytokeratin‐18 fragments were measured in situ via immunohistochemistry and in vivo using a novel enzyme‐linked immunosorbent assay. Plasma cytokeratin‐18 fragments were markedly increased in patients with NASH compared with patients with simple steatosis or normal biopsies (median [interquartile range]: 765.7 U/L [479.6–991.1], 202.4 U/L [160.4–258.2], 215.5 U/L [150.2–296.2], respectively; P < .001). Cytokeratin‐18 fragment levels independently predicted NASH (OR 1.95; 95% CI 1.18–3.22; P = .009 for every 50 U/L increase). A cutoff value of 395 U/L calculated using the receiver operating characteristic curve approach showed a specificity of 99.9%, a sensitivity of 85.7%, and positive and negative predictive values of 99.9% and 85.7%, respectively, for the diagnosis of NASH. In conclusion, these findings strongly suggest that determination of hepatocyte caspase activation in the blood is a strong and independent predictor of NASH in human subjects. These data highlight the potential usefulness of this test as a noninvasive diagnostic means of determining histological disease severity in patients with NAFLD. (HEPATOLOGY 2006;44:27–33.)

Cytokeratin-18 fragment levels as noninvasive biomarkers for nonalcoholic steatohepatitis: A multicenter validation study†

Liver biopsy remains the gold standard for diagnosing nonalcoholic steatohepatitis (NASH). We have recently demonstrated that plasma cytokeratin 18 (CK‐18) fragment levels correlate with the magnitude of hepatocyte apoptosis and independently predict the presence of NASH. The goal of this study was to validate the use of this biomarker for NASH diagnosis. The study was an ancillary study of the NASH Clinical Research Network (NASH CRN). Our cohort consisted of 139 patients with biopsy‐proven nonalcoholic fatty liver disease (NAFLD) from eight CRN participant centers across the United States and 150 age‐matched healthy controls. CK‐18 fragments were measured using a specific enzyme‐linked immunosorbent assay. Histology was assessed centrally by study pathologists. CK‐18 fragments were markedly increased in patients with NASH versus those without NASH and borderline diagnosis (median [25th, 75th percentile], 335 [196, 511], 194 [151, 270], 200 [148, 284], respectively; P < 0.001). Moreover, the odds of having fibrosis on liver biopsy increased with increasing plasma CK‐18 fragment levels (P < 0.001). On multivariate regression analysis, CK‐18 fragments remained an independent predictor of NASH after adjusting for variables associated with CK‐18 fragments or NASH on univariate analysis (fibrosis, alanine aminotransferase, aspartate aminotransferase, age, biopsy length). The area under the receiver operating characteristic curve for NASH diagnosis was estimated to be 0.83 (0.75, 0.91). Conclusion: Determination of CK‐18 fragments in the blood predicts histological NASH and severity of disease in a large, diverse population of patients with biopsy‐proven NAFLD, supporting the potential usefulness of this test in clinical practice. (HEPATOLOGY 2009.)

The natural history of non-alcoholic fatty liver disease in children: a follow-up study for up to 20 years.

Objectives: The long-term prognosis of non-alcoholic fatty liver disease (NAFLD) in children remains uncertain. We aimed at determining the long-term outcomes and survival of children with NAFLD. Design: Retrospective longitudinal hospital-based cohort study. Patients: Sixty-six children with NAFLD (mean age 13.9 (SD 3.9) years) were followed up for up to 20 years with a total of 409.6 person-years of follow-up. Results: The metabolic syndrome was present in 19 (29%) children at the time of NAFLD diagnosis with 55 (83%) presenting with at least one feature of the metabolic syndrome including obesity, hypertension, dyslipidaemia and/or hyperglycaemia. Four children with baseline normal fasting glucose developed type 2 diabetes 4–11 years after NAFLD diagnosis. A total of 13 liver biopsies were obtained from five patients over a mean of 41.4 (SD 28.8) months showing progression of fibrosis stage in four children. During follow-up, two children died and two underwent liver transplantation for decompensated cirrhosis. The observed survival free of liver transplantation was significantly shorter in the NAFLD cohort as compared to the expected survival in the general United States population of the same age and sex (log-rank test, p<0.00001), with a standardised mortality ratio of 13.6 (95% confidence interval, 3.8 to 34.8). NAFLD recurred in the allograft in the two cases transplanted, with one patient progressing to cirrhosis and requiring re-transplantation. Conclusions: Children with NAFLD may develop end-stage liver disease with the consequent need for liver transplantation. NAFLD in children seen in a tertiary care centre may be associated with a significantly shorter survival as compared to the general population.

Noninvasive diagnosis and monitoring of nonalcoholic steatohepatitis: present and future.

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the United States, and its prevalence is increasing worldwide. It currently affects approximately 30% of adults and 10% of children in the United States. NAFLD represents a wide spectrum of conditions ranging from simple fatty liver which in general follows a benign nonprogressive clinical course, to nonalcoholic steatohepatitis (NASH), which is a more serious form of NAFLD that may progress to cirrhosis and end‐stage liver disease. At present, a liver biopsy remains the only reliable way to diagnose NASH and establish the presence of fibrosis. Current noninvasive clinically available tests lack accuracy and reliability. In light of the dramatic increase in the prevalence of NAFLD in conjunction with the significant research effort in developing novel therapies for patients with NASH, noninvasive, simple, reproducible, and reliable biomarkers are greatly needed. They will not only help in the diagnosis of NASH, but also be useful for assessment of treatment response and prognosis and remain a research priority in the NAFLD field. (HEPATOLOGY 2007;46:582–589.)

Increased Hepatic and Circulating Interleukin-6 Levels in Human Nonalcoholic Steatohepatitis

BACKGROUND:Nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes (T2D) are growing public health problems, and are strongly associated. The link between the two conditions remains poorly understood. Hepatic interleukin-6 (IL-6), a major proinflammatory cytokine, expression is increased in animal models of NAFLD, while in mice, selective sustained upregulation of IL-6 in the liver results in systemic insulin resistance. The extent and clinical significance of hepatic IL-6 expression in human NAFLD, as well as potential mechanisms by which steatosis may increase IL-6 production in the liver, have not been examined.AIMS:To ascertain the occurrence and significance of IL-6 expression in the liver in human NAFLD.PATIENTS AND METHODS: Plasma was obtained at time of liver biopsy from 50 consecutive patients with suspected NAFLD. Histology was assessed blindly. Hepatic IL-6 expression was assessed by immunohistochemistry, while plasma IL-6 levels were determined by an enzyme-linked immunosorbent assay.RESULTS:IL-6 expression was markedly increased in the livers of patients with nonalcoholic steatohepatitis (NASH) as compared to patients with simple steatosis (P < 0.005) or normal biopsies (P < 0.010), confirming the presence of hepatic IL-6 expression in human NASH. A positive correlation was observed between hepatocyte IL-6 expression and degree of inflammation and stage of fibrosis. Furthermore, liver IL-6 expression positively correlated with plasma IL-6 levels and degree of systemic insulin resistance. Culture of liver cells with saturated, but not mono- or polyunsaturated, FFA resulted in a significant increase in IL-6 messenger RNA (mRNA) and protein expression.CONCLUSION:Collectively, these data suggest that increased hepatic IL-6 production may play an important role in NASH development, as well as in systemic insulin resistance and diabetes.

Hepatic Lipid Partitioning and Liver Damage in Nonalcoholic Fatty Liver Disease ROLE OF STEAROYL-CoA DESATURASE

Hepatic lipid overloading mainly in the form of triglycerides is considered a prerequisite for the development of nonalcoholic fatty liver disease (NAFLD). However, triglyceride accumulation in the liver in response to lipid overflow may represent a protective mechanism against lipotoxicity. Our aims were to assess the fundamental cellular mechanisms that link lipid compartmentation in hepatocytes to liver damage and disease progression in NAFLD by using both in vivo dietary models of NAFLD and in vitro cell models of lipid overloading. Exposure of murine or human hepatocytes to monounsaturated fatty acids (MUFAs) resulted in lipid accumulation without changes in cell viability. In contrast, cell incubation with saturated fatty acids (SFAs) significantly decreased cell viability and increased caspase activation and apoptosis, with only minor lipid droplet accumulation. Genetic or pharmacological inhibition of stearoyl-CoA desaturase-1 (SCD1), the enzyme that converts SFA to MUFA, sensitized cells to SFA-induced apoptosis. Hepatic SCD1 expression increased in experimental steatosis resulting from high fat diet and decreased in a methionine-choline-deficient (MCD) dietary model of steatohepatitis resulting in the latter situation in significantly increased hepatic SFA levels. SCD1–/– mice on the MCD diet had decreased steatosis and markedly increased hepatocellular apoptosis, liver injury, and fibrosis compared with the SCD1+/+, whereas MUFA feeding prevents the MCD-induced injury. In conclusion, this study suggests hepatic SCD1 plays a key role in prevention of steatohepatitis by partitioning excess lipid into MUFA that can be safely stored. This concept has important implications for the development of novel treatment strategies for patients with this condition.

From NAFLD to NASH to cirrhosis—new insights into disease mechanisms

NAFLD has evolved as a serious public health problem in the USA and around the world. In fact, NASH—the most serious form of NAFLD—is predicted to become the leading cause of liver transplantation in the USA by the year 2020. The pathogenesis of NAFLD and NASH, in particular the mechanisms responsible for liver injury and fibrosis, is the result of a complex interplay between host and environmental factors, and is at the centre of intense investigation. In this Review, we focus on recently uncovered aspects of the genetic, biochemical, immunological and molecular events that are responsible for the development and progression of this highly prevalent and potentially serious disease. These studies bring new insight into this complex disorder and have led to the development of novel therapeutic and diagnostic strategies that might enable a personalized approach in the management of this disease.