Unravelling Mechanisms of Fructose vs Glucose Consumption in the Pathogenesis and Progression of NAFLD

Unravelling the Pathogenetic Mechanisms of Fructose in Comparison to Glucose Consumption as Multiple Hit in the Pathogenesis and Progression of Non-alcoholic Fatty Liver Disease (NAFLD) - an Exploratory Trial

Non-alcoholic fatty liver disease (NAFLD) comprises a spectrum ranging from simple fatty liver over steatohepatitis (NASH) to liver cirrhosis and cancer (HCC) and is a major and increasing health problem affecting nearly 40% of the general population. Moreover, NAFLD is an important risk factor for progression of diabetes and atherosclerosis. However, the pathomechanisms determining disease progression are poorly understood. The overall aim of this project is to test the central hypothesis that excessive fructose consumption provides a multiple metabolic hit in the pathogenesis and progression of NAFLD/NASH by impairment of hepatic lipid homeostasis and mitochondrial function resulting in hepatic lipotoxicity with inflammasome activation and disturbed interorgan cross-talk among insulin sensitive tissues.

To achieve these goals we will address the following specific hypotheses that

• Fructose-induced changes in lipid composition of hepatocellular stores determine lipotoxicity which may be associated with abnormalities in mitochondrial function, energy homeostasis, inflammasome activation and cellular injury in progression to NASH, effects which will be compared to glucose
• Non-invasive characterization of fructose (compared to glucose)-induced lipotoxic hepatic and extrahepatic metabolic risk profiles (lipid composition and energy metabolism) obtained by magnetic resonance spectroscopy (MRS) will identify patients with NASH
• Severity of fructose (compared to glucose)-induced lipotoxic lipid and adenosine triphosphate (ATP) derangements (identified by MRS) critically determines the degree of insulin resistance and abnormalities in hepatic glucose and lipid metabolism
• Compensatory hyperinsulinemia, secondary to skeletal muscle insulin resistance, may be a primary mechanism of hepatic lipotoxicity and progression to NASH
• Gender differences in the hepatic and systemic metabolic response to fructose are mediated by the impact of female sex hormones and their nuclear receptors on hepatic lipid metabolism, mitochondrial function and inflammasome activation.
• Age differences in the hepatic and systemic metabolic response to fructose are mediated by the impact of age related alterations on hepatic lipid metabolism and mitochondrial function.

These key hypotheses will be addressed by a translational research consortium including hepatologists, radiologists, physicists, endocrinologists and specialist in gender medicine allowing an integrated mechanistic approach to NAFLD. The strength of the current proposal comes directly from bridging basic science and clinical perspectives of different disciplines involved in the management of NAFLD, including cutting edge non-invasive technologies such as high field MRS metabolic profiling ('virtual metabolic liver biopsy') and mechanistic in vitro experiments. This project will provide novel mechanistic insights in the role of fructose as emerging hepatic 'toxin' in the pathogenesis and progression of NASH, as increasing health problem in Western society. Moreover, this study will clarify the impact of sex and gender on fructose-induced alterations in hepatic and systemic metabolism, providing a rational and scientific basis for future dietary interventions and regulatory actions.

Inclusion criteria

1. Healthy men and women from 18 to 85, no disease history, no intake of regular medication, drugs, alcohol (alcohol consumption > 140 grams per week (or > 30g/day) 45) or herbals known to affect liver physiology, male and female (1:1), BMI <= 25.
2. Patients with prior confirmed (biopsy within 6 months prior to study) intrahepatic fat accumulation/simple fatty liver (NAFL), HbA1c < 6.5, male and female (1:1)
3. Patients with confirmed NASH (biopsy within 6 months prior to study), HbA1c < 6.5, male and female (1:1).
4. Signed informed consent, willing and able to perform study procedures.

General exclusion criteria (for all groups)

1. Pregnancy and lactation (blood/urine pregnancy test will be performed for female volunteers at baseline and week 4)
2. Imprisoned persons
3. Declined informed consent
4. Inflammatory bowel conditions (celiac disease, Crohn's disease, ulcerative colitis)
5. Prior bariatric surgery
6. Alcoholic steatohepatitis and/or alcohol consumption > 140 grams per week (or > 30g/day) 45
7. Other liver diseases (autoimmune, genetic, cholestatic, Wilson disease, Weber-Christian disease, partial lipodystrophy of the face sparing type, abetalipoproteinemia, and jejunal diverticulosis with bacterial overgrowth).
8. Virus hepatitis (A, B, C)
9. Known allergic reaction to the drugs used (see material and methods)
10. Intake of drugs known to accumulate intrahepatic lipids and significantly interfere with metabolism (e.g. steroids/glucocorticoids, tamoxifen, amiodarone, perhexiline maleate, antiretroviral agents, tetracycline, minocycline, certain pesticides) 45
11. Inability or contraindications to perform study procedures
12. Fructose malabsorption diagnosed by two consecutive positive fructose hydrogen breath test

MRI contraindications Study participants with claustrophobia Study participants carrying

• a cardiac pacemaker
• an insulin pump
• operation clips
• nerval stimulators
• implants or prostheses (e.g. ear implants, hip prostheses, heart valve, penile prosthesis)
• metal parts or metal fragments [e.g. metallic intrauterine devices (IUDs), marrow nail, metallic splinters or munition rests)
• metallic shunts or stents