GW BGZ2026 Case 4 - In the hepatologist´s practice

How are carbohydrates (especially glucose, galactose, and fructose) absorbed in the intestine?

Carbohydrate uptake occurs in a highly coordinated transporter system in the small intestine:

• Glucose & galactose uptake

  • Via SGLT1 (Sodium-Glucose Linked Transporter 1)

  • Uses Na⁺ gradient (secondary active transport)

  • Allows absorption even against glucose gradient

• Fructose uptake

  • Via GLUT5

  • Facilitated diffusion (no energy required)

• Exit into bloodstream

  • All monosaccharides leave enterocytes via GLUT2

  • Enter portal circulation → liver first-pass metabolism

Key concept:

• Intestinal absorption is transporter-specific and energy-dependent (for glucose/galactose) but passive for fructose

How is glucose transported in blood and stored in the body?

Glucose transport and storage are highly regulated to maintain blood glucose homeostasis:

• Transport in blood

  • Glucose is freely soluble in plasma

  • Does NOT require carriers in blood (unlike lipids)

• Storage forms

  • Glycogenesis (glycogen synthesis):

    • Liver → maintains blood glucose levels between meals

    • Muscle → local energy reserve (not released into blood)

• Excess glucose fate

  • Converted into fatty acids (lipogenesis) in liver

  • Stored as triglycerides in adipose tissue

Key concept:

• Glucose is a short-term energy buffer, while fat is long-term energy storage

How are dietary lipids absorbed and transported in the body?

Lipid absorption requires emulsification and packaging due to their hydrophobic nature:

• Digestion in intestine

  • Bile acids emulsify fat droplets

  • Pancreatic lipase breaks triglycerides → fatty acids + monoacylglycerols

• Absorption in enterocytes

  • Re-esterification → triglycerides reform inside cells

• Transport in blood

  • Packaged into lipoproteins:

    • Chylomicrons → dietary fat transport

    • VLDL → liver-derived triglycerides

• Delivery to tissues

  • Lipoprotein lipase (LPL) breaks TG → free fatty acids

  • Fatty acids taken up by muscle/adipose tissue

Key concept:

• Lipids require structural packaging (lipoproteins) for transport in aqueous blood

How is glucose metabolized in glycolysis?

Glycolysis is the cytosolic pathway that converts glucose into energy:

• Main purpose

  • Glucose → pyruvate + ATP + NADH

• Key regulatory step

  • Fructose-6-P → Fructose-1,6-bisP via PFK-1

  • This is the rate-limiting enzyme

• Energy yield

  • Net: 2 ATP + 2 NADH per glucose

• Fate of pyruvate

  • Aerobic → acetyl-CoA (mitochondria)

  • Anaerobic → lactate (regenerates NAD⁺)

Key concept:

• Glycolysis is fast ATP production, especially important in hypoxia or high demand

How are free fatty acids metabolized (β-oxidation)?

β-oxidation breaks down fatty acids into energy-rich acetyl-CoA units:

• Step 1: Activation

  • Fatty acid → fatty acyl-CoA (ATP-dependent)

• Step 2: Transport

  • Carnitine shuttle via CPT-1 (rate-limiting step)

• Step 3: β-oxidation cycle

  • Each cycle produces:

    • Acetyl-CoA

    • NADH

    • FADH₂

• Outcome

  • High ATP yield after oxidative phosphorylation

Key concept:

• Fatty acids are a high-energy, slow-burning fuel source

What is the role of the citric acid (TCA) cycle?

The TCA cycle is the central hub of energy metabolism:

• Location

  • Mitochondrial matrix

• Function

  • Oxidizes acetyl-CoA → CO₂

• Energy output per acetyl-CoA

  • 3 NADH

  • 1 FADH₂

  • 1 GTP (ATP equivalent)

• Importance

  • NADH/FADH₂ feed into oxidative phosphorylation → major ATP production

Key concept:

• TCA cycle is the final common pathway for carbohydrate and fat metabolism

What is ectopic fat and why is it metabolically harmful?

Ectopic fat is lipid storage in non-adipose tissues due to overflow from adipose tissue:

• Normal storage site

  • Adipose tissue (safe triglyceride storage)

• Ectopic sites

  • Liver → fatty liver (MASLD)

  • Muscle → insulin resistance

  • Pancreas → β-cell dysfunction

• Mechanism of toxicity

  • Lipid overload → DAGs + ceramides

  • These interfere with insulin signaling pathways

• Clinical consequences

  • Type 2 diabetes

  • Metabolic syndrome

  • NAFLD/MASH

Key concept:

• Fat becomes harmful when storage capacity is exceeded

Is dietary fat harmful or beneficial?

The effect of dietary fat depends on type and metabolic context:

• Harmful fats

  • Saturated fats → ↑ LDL cholesterol

  • Trans fats → inflammation + cardiovascular risk

• Beneficial fats

  • MUFA (olive oil) → improves lipid profile

  • PUFA (omega-3) → anti-inflammatory effects

• Modern understanding

  • Total energy balance matters more than fat alone

  • Overnutrition → fat accumulation regardless of source

Key concept:

• Dietary fat is not inherently bad—metabolic context determines outcome

How are carbohydrate and fat metabolism integrated?

Carbohydrate and fat metabolism are tightly interconnected energy systems:

• Fed state (high insulin)

  • Glucose → glycogen + fat (lipogenesis)

  • Energy storage dominates

• Fasted state (low insulin, high glucagon)

  • Fatty acids → β-oxidation

  • Glucose spared for brain

• Metabolic convergence

  • Both pathways produce acetyl-CoA

  • Enter TCA cycle for ATP production

Key concept:

• Energy metabolism is state-dependent (fed vs fasting) and highly flexible

What are the main causes and risk factors of obesity?

Lifestyle / environmental factors (majority ~60–70%)

• Excess calorie intake (energy surplus)

• Ultra-processed foods (high sugar/fat, low fiber)

• Sugary drinks + large portions

• Physical inactivity (low NEAT, sedentary behavior)

• Poor sleep / circadian disruption

• Stress → emotional eating

• “Obesogenic environment” (cheap, available high-calorie food)

Biological / genetic factors (~30–40%)

• Polygenic risk (most common)

• Rare monogenic obesity (e.g., leptin pathway defects)

• Family history

Medical factors

• Hypothyroidism, Cushing syndrome

• Medications (antipsychotics, corticosteroids, some antidepressants, SSRIs)

key idea: Obesity results from energy imbalance + susceptibility (genetic + biological)

What are the consequences of obesity?

Obesity affects multiple organ systems through insulin resistance and inflammation.

Metabolic

• Insulin resistance → type 2 diabetes

• Dyslipidaemia (↑ TG, ↓ HDL)

• Metabolic syndrome

Cardiovascular

• Hypertension

• Atherosclerosis

• ↑ MI and stroke risk

Liver

• MASLD → MASH → fibrosis → cirrhosis

Other effects

• Sleep apnea, osteoarthritis

• Infertility / hormonal changes

• Increased cancer risk (colon, breast, endometrial)

• Depression and reduced quality of life

Key idea: Obesity is a systemic inflammatory + metabolic disease

How does obesity lead to type 2 diabetes?

Obesity causes insulin resistance, which eventually leads to β-cell failure.

Process

• Visceral fat releases FFAs → insulin resistance

• Cytokines (TNF-α, IL-6) → inflammation

• Muscle ↓ glucose uptake

• Liver ↑ glucose production

Progression

1. Insulin resistance

2. Hyperinsulinaemia (compensation)

3. β-cell exhaustion

4. Persistent hyperglycaemia → T2D

Key idea:

T2D = failure of pancreatic compensation

How are obesity, diabetes, and hypertension linked?

They are different outcomes of the same underlying process: insulin resistance.

Core mechanism

• Obesity → visceral fat inflammation

• Insulin resistance develops

Effects

• T2D: β-cell failure → hyperglycaemia

• Hypertension:

  • ↑ sympathetic activity

  • RAAS activation

  • Na⁺ retention

  • Endothelial dysfunction

Key idea:

One disease network = metabolic syndrome

Why is obesity central in metabolic disease?

Obesity is the upstream driver of most metabolic and cardiovascular disease.

Clinical effects

• Insulin resistance → T2D

• Dyslipidaemia → atherosclerosis

• Liver fat → MASLD/MASH

• Hypertension → vascular dysfunction

Markers in patients

• High BMI + waist circumference

• ↑ glucose

• ↑ triglycerides

• ↑ liver enzymes (ALT/AST)

Key idea:

Treating obesity addresses the root cause of metabolic disease

What is Metabolic dysfunction-associated steatohepatitis (MASH, formerly NASH)?

• MASH (Metabolic dysfunction-associated steatohepatitis) is the inflammatory form of MASLD (Metabolic dysfunction-associated steatotic liver disease).

• It develops when fat accumulation (≥5% of hepatocytes) is accompanied by:

  • Hepatocyte injury

  • Inflammation

  • Fibrosis (scar formation)

• MASH can progress to:

  • Cirrhosis

  • Liver failure

  • Hepatocellular carcinoma

Association

• Considered the hepatic manifestation of metabolic syndrome.

• Strongly associated with:

  • Obesity

  • Type 2 diabetes

  • Hypertension

  • Dyslipidaemia

  • Insulin resistance

How does MASH develop?

The multiple-hit hypothesis explains that several mechanisms occur simultaneously:

• Insulin resistance

  • Increased lipolysis

  • More free fatty acids (FFAs) delivered to the liver

  • Increased de novo lipogenesis

  • Causes hepatic steatosis

• Lipotoxicity

  • Toxic lipids (ceramides and diacylglycerols) damage hepatocytes

  • Leads to mitochondrial dysfunction, ER stress and apoptosis

• Oxidative stress

  • Fat accumulation increases ROS production

  • CYP2E1 further increases ROS

  • ROS damages DNA, proteins and lipids

• Chronic inflammation

  • Damaged hepatocytes activate Kupffer cells

  • Cytokines released:

    • TNF-α

    • IL-6

    • IL-1β

• Fibrosis

  • Stellate cells become activated

  • Produce collagen

  • Fibrosis may progress to cirrhosis

• Gut microbiome

  • Dysbiosis increases intestinal permeability

  • LPS enters portal circulation

  • Further promotes inflammation and fibrosis

Explain the role of CYP2E1 in MASH.

CYP2E1 contributes to oxidative liver injury.

• Upregulated in fatty liver disease.

• Produces reactive oxygen species (ROS) during fatty acid metabolism.

• ROS causes:

  • Lipid peroxidation

  • Mitochondrial damage

  • ER stress

  • Hepatocyte injury

Key pathway

CYP2E1 → ROS → Oxidative stress → MASH

How does obesity contribute to MASH?

Obesity promotes MASH through several mechanisms:

• Causes insulin resistance

• Increases release of free fatty acids

• Increases liver fat accumulation

• Alters the gut microbiome (dysbiosis)

• Increases gut permeability

• Allows LPS to enter the liver

• Promotes chronic inflammation

• Reduces adiponectin

• Increases leptin, promoting fibrosis

Describe the progression from fatty liver to cirrhosis.

The progression occurs in several stages:

1. Steatosis

   • Fat accumulates in hepatocytes.

2. Steatohepatitis (MASH)

   • Lipotoxicity

   • Oxidative stress

   • Inflammation

3. Cell death

   • Apoptosis and necrosis

   • DAMP release

4. Fibrosis

   • Activation of hepatic stellate cells

   • Collagen deposition

5. Cirrhosis

   • Extensive scarring

   • Nodular liver

   • Liver failure risk

What are the major risk factors for MASH?

Major risk factors include:

• Obesity (especially visceral obesity)

• Type 2 diabetes

• Insulin resistance

• Metabolic syndrome

• Hypertension

• Hypertriglyceridaemia

• Sedentary lifestyle

• High-fat and high-fructose diets

• Genetic variants:

  • PNPLA3

  • TM6SF2

What is metabolic syndrome and its main mechanism?

Metabolic syndrome is a cluster of risk factors driven by insulin resistance and visceral obesity.

Criteria (≥3):

• Abdominal obesity

• ↑ triglycerides

• ↓ HDL

• Hypertension

• ↑ fasting glucose / T2D

Mechanism

• Visceral fat → ↑ FFAs + cytokines (TNF-α, IL-6)

• ↓ adiponectin → reduced insulin sensitivity

• Chronic low-grade inflammation

Effects

• Endothelial dysfunction → hypertension

• Insulin resistance → T2D

• Liver fat accumulation → MASLD/MASH

Key idea: Metabolic syndrome = insulin resistance + visceral fat inflammation

What type of inflammation occurs in metabolic syndrome?

The inflammation is chronic low-grade systemic inflammation.

Characteristics include:

• Continuous immune activation

• No acute infection present

• Increased inflammatory cytokines:

  • TNF-α

  • IL-6

  • IL-1β

  • MCP-1

This inflammation worsens:

• Insulin resistance

• Endothelial dysfunction

• Atherosclerosis

• Liver fibrosis

What are the diagnostic criteria for metabolic syndrome?

Diagnosis requires 3 or more of the following:

• Central obesity

• Triglycerides ≥1.7 mmol/L

• Low HDL cholesterol

• Blood pressure ≥130/85 mmHg

• Fasting glucose ≥5.6 mmol/L or type 2 diabetes

How is MASH diagnosed?

Diagnosis requires a combination of:

History & Examination

• Obesity

• Diabetes

• Hypertension

• Hepatomegaly

• Blunt liver edge

Blood tests

• ALT

• AST

• GGT

• Ferritin

• Glucose

• Lipid profile

Imaging

• Ultrasound

• FibroScan

• MRI-PDFF

Fibrosis assessment

• FIB-4

• NAFLD Fibrosis Score

• ELF test

Gold standard

• Liver biopsy

What is the significance of ALT and AST in MASH?

ALT

• More liver-specific.

• Usually higher than AST in early disease.

AST

• Found in liver, muscle and heart.

• Often becomes higher than ALT in advanced fibrosis or cirrhosis.

Important limitation

• ALT and AST cannot distinguish simple steatosis from MASH.

• Normal values do not exclude disease.

What imaging techniques are used in MASH?

• Ultrasound

  • First-line investigation.

  • Detects moderate-to-severe steatosis.

• FibroScan

  • Measures liver stiffness.

  • Estimates fibrosis.

  • Measures steatosis using CAP.

• MRI-PDFF

  • Most accurate for liver fat quantification.

• CT

  • Can detect fatty liver but is rarely used.

How is type 2 diabetes treated in patients with MASH?

Main medications include:

• Metformin

  • Improves insulin sensitivity.

  • Reduces hepatic gluconeogenesis.

• GLP-1 receptor agonists (e.g. Semaglutide)

  • Weight loss

  • Improves insulin resistance

  • Reduces liver fat

  • Improves steatohepatitis

• SGLT2 inhibitors

  • Weight loss

  • Cardio-renal protection

  • Reduces liver fat

• Pioglitazone

  • Improves MASH histology

  • May cause weight gain

• DPP-4 inhibitors

  • Weight neutral

  • Mild glucose lowering

  • Little benefit for MASH

How do DPP-4 inhibitors work?

Mechanism

• Inhibit the DPP-4 enzyme.

• Prevent breakdown of:

  • GLP-1

  • GIP

This results in:

• Increased glucose-dependent insulin secretion.

• Reduced glucagon secretion.

Advantages

• Low hypoglycaemia risk.

• Weight neutral.

Disadvantages

• Minimal weight loss.

• Little improvement in liver fat or fibrosis.

Why are GLP-1 receptor agonists beneficial in MASH?

GLP-1 receptor agonists:

• Increase glucose-dependent insulin secretion.

• Reduce glucagon.

• Slow gastric emptying.

• Increase satiety.

Clinical benefits:

• Significant weight loss.

• Improved insulin sensitivity.

• Reduced hepatic steatosis.

• Reduced inflammation.

• Lower cardiovascular risk.

They directly target the underlying metabolic dysfunction driving MASH.

What is the cornerstone treatment for MASH?

Weight loss is the cornerstone of treatment.

Benefits include:

• ≥5% weight loss

  • Improves steatosis.

• 7–10% weight loss

  • Improves inflammation.

  • Improves hepatocyte ballooning.

• ≥10% weight loss

  • May improve fibrosis.

Lifestyle changes include:

• Mediterranean diet.

• Caloric restriction.

• Aerobic exercise.

• Resistance training.

What is the role of Vitamin E, Vitamin C and UDCA in MASH?

Vitamin E

• Antioxidant.

• Reduces oxidative stress.

• Improves steatosis and inflammation.

• Limited benefit in patients with diabetes.

Vitamin C

• Antioxidant.

• Regenerates Vitamin E.

• Limited evidence for improving MASH.

UDCA

• Hydrophilic bile acid.

• Protects hepatocytes.

• Improves bile flow.

• Not recommended as standard treatment because it has not consistently improved MASH histology.

What are the main therapeutic priorities in a patient with MASH?

Treatment aims to address the underlying metabolic dysfunction:

• Weight loss (most important intervention)

• Improve insulin resistance

  • Metformin

  • GLP-1 receptor agonists

• Reduce cardiovascular risk

  • Control blood pressure

  • Manage dyslipidaemia

• Slow liver disease progression

• Prevent cirrhosis and liver failure

The overall goal is to reverse steatosis, reduce inflammation, and prevent fibrosis progression.

Interpret these liver tests

• Enzymes involved in mitochondria in liver.

• Serum Transaminases

  • Hepatocyte damage (viral hepatitis, (N)AFLD, etc.)

  • Aspartate aminotransferase (AST)

    • Heart, muscle, kidney, brain

  • Alanine aminotransferase (ALT)

    • More liver specific, ALT usually higher than AST (except in alcoholic liver disease)

• Cholestatic liver tests

  • Biliary obstruction (primary billiary cholangitis, bile duct stone/tumor, etc.)

  • Alkaline phospatase

    • Bone, liver, (placenta, intestine)

    • General enzyme

  • Gamma-glutamyl transpeptidase (G-GT)

    • Hepatocytes, biliary epithelial cells, kidney, seminal vesicles, pancreas, spleen, heart and brain.

  • Bilirubin

    • Think at prehepatic (hemolysis), hepatic, post-hepatic causes (cholestasis)

• Liver function tests: INR, albumin and in advanced liver disease also bilirubin

The diagnosis

• Alcoholic liver disease (ALD)

• Metabolic dysfunction associated steatotic liver disease (MASLD)

What is liver cirrhosis?

Liver cirrhosis is the end stage of chronic liver disease.

Characteristics include:

• Progressive fibrosis.

• Replacement of healthy liver tissue with scar tissue.

• Distortion of normal liver architecture.

• Reduced liver volume.

• Vascular remodeling leading to portal hypertension.

Complications include:

• Liver failure

• Portal hypertension

• Ascites

• Variceal bleeding

• Hepatocellular carcinoma

How does fibrosis develop?

Fibrosis develops following repeated liver injury.

The process involves:

• Chronic hepatocyte injury.

• Activation of hepatic stellate cells.

• Transformation into collagen-producing myofibroblasts.

• Progressive deposition of connective tissue.

• Development of cirrhosis if injury continues.

What are the Milan criteria for liver transplantation in hepatocellular carcinoma?

Patients qualify if they meet all of the following:

• One tumour ≤5 cm, or

• Up to three tumours, each ≤3 cm

• No vascular invasion

• No extrahepatic metastases

Meeting these criteria gives good post-transplant survival.

What are the requirements for orthotopic liver transplantation (OLT)?

Patients should have:

• No alcohol use for at least 6 months

• HCC within Milan criteria

• Good physical condition:

  • No severe obesity

  • No sarcopenia

  • No chronic infection

  • No active viral hepatitis

How does the Western lifestyle contribute to MASLD?

The Western lifestyle promotes obesity and insulin resistance through:

• High-calorie diets.

• Excess carbohydrates.

• High saturated fat intake.

• High fructose consumption.

• Processed foods.

• Low fibre intake.

• Low antioxidant intake.

• Alcohol consumption.

• Physical inactivity.

These factors promote visceral obesity, fat accumulation, and chronic inflammation.

Why is visceral fat more harmful than subcutaneous fat?

Visceral fat is metabolically active and acts as an endocrine organ.

It:

• Releases free fatty acids.

• Produces inflammatory cytokines.

• Promotes insulin resistance.

• Alters adipokine production.

• Increases risk of:

  • Type 2 diabetes

  • MASLD

  • Cardiovascular disease

What are the major functions of the liver?

The liver maintains homeostasis through several functions.

Metabolic functions

• Carbohydrate metabolism.

• Protein metabolism.

• Lipid metabolism.

Synthetic functions

• Albumin production.

• Clotting factor synthesis.

• Bile salt production.

Detoxification

• Drugs.

• Alcohol.

• Toxins.

Storage

• Glycogen.

• Iron.

• Copper.

• Vitamin B12.

Immune function

• Filters bacteria and endotoxins from portal blood.

What are the main pathogenetic factors in MASLD?

The most important mechanisms include:

• Insulin resistance (hallmark).

• Dyslipidaemia.

• Oxidative stress.

• Gut dysbiosis.

• Muscular dysfunction.

Together they promote:

• Steatosis.

• Inflammation.

• Fibrosis.

Which factors aggravate MASLD?

Important aggravating factors include:

• Poor diet.

• Obesity.

• Alcohol.

• Drugs.

• Genetic variants:

  • PNPLA3

  • TM6SF2

• Gut microbiome alterations.

• Increased intestinal permeability.

• Viral hepatitis.

• Environmental toxins.

Why is the gut microbiome important in MASLD?

The gut-liver axis contributes to liver inflammation.

Mechanisms include:

• Gut dysbiosis.

• Increased intestinal permeability.

• Leakage of lipopolysaccharide (LPS).

• Bacterial overgrowth.

• Increased endogenous alcohol production.

These processes activate liver inflammation and fibrosis.

What is the most important prognostic factor in MASLD?

The strongest predictor of long-term outcome is:

• Fibrosis stage

Advanced fibrosis is associated with:

• Increased liver-related mortality.

• Greater risk of cirrhosis.

• Increased hepatocellular carcinoma.

• Increased cardiovascular mortality.

What is the leading cause of death in patients with MASLD?

Most patients with MASLD do not die from liver disease.

The leading cause of death is:

• Cardiovascular disease

Examples include:

• Myocardial infarction.

• Stroke.

• Coronary artery disease.

Risk increases further in patients with advanced fibrosis.

Why is MASLD considered a multisystem disease?

MASLD affects many organs because it is driven by chronic low-grade systemic inflammation.

Associated diseases include:

• Type 2 diabetes.

• Cardiovascular disease.

• Chronic kidney disease.

• Metabolic syndrome.

• Obesity.

• Hepatocellular carcinoma.

How does FibroScan work?

FibroScan is a non-invasive ultrasound-based technique.

It measures:

• Liver stiffness

  • Indicates fibrosis.

• Controlled Attenuation Parameter (CAP)

  • Estimates liver fat (steatosis).

It is widely used because it is:

• Quick.

• Painless.

• Repeatable.

• More practical than liver biopsy.

What is the stepwise treatment approach for MASLD?

Management follows a stepwise approach:

1. Lifestyle intervention

   • Weight loss.

   • Healthy diet.

   • Physical activity.

2. Medical therapy

   • GLP-1 receptor agonists.

   • Other metabolic drugs when indicated.

3. Bariatric surgery

   • Considered for severe obesity when lifestyle measures fail.

What are the benefits of GLP-1 receptor agonists in MASLD?

Examples include Semaglutide (Ozempic, Wegovy, Rybelsus).

Benefits include:

• Significant weight loss.

• Reduced hepatic steatosis.

• Reduced liver inflammation.

• Improved glucose control.

• Lower HbA1c.

• Improved lipid profile.

• Reduced cardiovascular events.

They are most effective when combined with lifestyle modification.

What is Resmetirom and how does it work?

Resmetirom is a thyroid hormone receptor-β agonist approved in the USA for selected patients with MASH.

Its effects include:

• Improving lipid metabolism.

• Increasing β-oxidation.

• Reducing hepatic fat.

• Promoting MASH resolution.

• Improving fibrosis in some patients.

It represents one of the first targeted drug therapies for MASH.