CHEMICAL PATHOLOGY OF LIVER DISEASES

Question 1

What are the zones of the liver acinus?
Which zone is most involved in drug metabolism and most susceptible to drug-induced damage?

Answer 1

Based on the differential blood flow to the acinus, it is divided into 3 functional zones
* periportal highest oxygen content: this zone is least susceptible to ischaemic attack
* mediolobular intermediate
* centrilobular lowest oxygen content, most susceptible to ischaemic damage.
This zone is most involved in drug metabolism, most susceptible to drug-induced damage

Question 2

What are the metabolic functions of the liver?

Answer 2

Glycolysis, the Krebs cycle, gluconeogenesis, glycogen synthesis and glycogenolysis, lipogenesis, ketogenesis, amino acid synthesis and degradation, and protein synthesis all take place in the hepatocytes.

Hepatocytes also metabolise and detoxify endogenous (haem) and exogenous products (drugs), which are then excreted via the biliary tree

Question 3

What are the sources of bilirubin?

Answer 3

1. Haemoglobin : The breakdown of RBC releases haemoglobin
2. It is also released from and an ineffective erythropoiesis
3. Other haem containing proteins e.g. myoglobin and cytochrome P450

About 70 to 80% of daily bilirubin production is derived from the breakdown of senescent (old) red blood cells, while the remainder is derived from ineffective erythropoiesis and the breakdown of other haem-containing proteins.

Question 4

How is Bilirubin formed and metabolized?
Why is bilirubin neurotoxic?

Answer 4

Globin and Haem are formed from breaking down of haemoglobin
Globin (a protein) is broken down to its constituent amino acids.

Haem (a 4 ring structure containing Fe at its centre) is broken down (via biliverdin) to carbon monoxide, iron and bilirubin.
The bilirubin at this stage is termed unconjugated bilirubin.

Unconjugated bilirubin is hydrophobic in nature strongly bind to albumin in it hydrophobic site

Some drugs displace it from its albumin binding site e.g salicylate or any of the sulphonamides.
It is highly neurotoxic causing kernicterus when deposited in the cell membranes of basal ganglia

Question 5

How is Unconjugated Bilirubin metabolized?

Answer 5

Unconjugated Bilirubin Uptake by the Liver
The unconjugated bilirubin - albumin complex is carried in the plasma to the hepatic sinusoids.
Within the hepatocyte the unconjugated bilirubin is bound to ligandin

Question 6

How is Conjugated Bilirubin formed and then metabolized?

What is the rate limiting step of this process?

Answer 6

Conjugation of Bilirubin by the Liver

• The bilirubin is then conjugated with glucuronic acid by UDP-glucuronyl transferase (UDPGT I) to bilirubin monoglucuronide (BMG) and by UDPGT II to bilirubin diglucuronide (BDG).
• Conjugated bilirubin is more water soluble
• Conjugated bilirubin is transported out of the liver cells into the bile canaliculi
  This is a rate -limiting step in bilirubin metabolism
• Bilirubin along with bile flows through the canaliculi, into the bile ducts, and finally into the duodenum

Question 7

What happens to bilirubin in the GIT?

What then happens to urobilinogen?

Clinical correlate of urobilinogen?

Answer 7

In the GIT, bacterial flora convert conjugated bilirubin to urobilinogen.

Most of the urobilinogen (colourless) is further converted by colon bacteria to urobilin and stercobilin (brown).

About 20% of urobilinogen in the small intestine is reabsorbed into the portal circulation and re-excreted back to the intestine (enterohepatic circulation).

Some urobilinogen appears in normal urine but becomes excess if re-uptake is defective as a result of liver damage or an increased bilirubin production

Question 8

What are the primary bile acids?
What are the secondary bile acids?
How are bile acids conjugated & metabolized?

Answer 8

The primary bile acids are chenodeoxycholic acid and cholic acid, they are metabolic products of cholesterol from the liver.

The primary bile acids are made more soluble by conjugation with glycine or taurine.

Conjugated bile acids are transported out of the liver cells into the bile canaliculi

In the GIT, bacterial enzymes deconjugate and α dehydroxylate the primary bile acids and convert them to the secondary bile acids lithocholic acid and deoxycholic acid.

Most of the bile acids in the GIT are reabsorbed into the portal circulation (75% in the ileum and 10% in the colon), taken up by the liver again and re-excreted (enterohepatic circulation).

Normally a small amount escapes into the systemic circulation.

Any form of obstruction of biliary tree causes reflux of bile acid in the system

Question 9

What is Normal serum total bilirubin?

Answer 9

<17 μmol/l

Question 10

Does normal urine contain bilirubin and why?

Answer 10

Normal urine contains no bilirubin, since unconjugated bilirubin is albumin-bound and not filtered.

Question 11

Increased amounts of unconjugated bilirubin are found in plasma in:

Answer 11

. Increased bilirubin production
. Decreased uptake or conjugation of bilirubin
. in generalised hepatocellular dysfunction
. in specific rare inherited syndromes (Gilbert’s and Criggler-Najjar syndromes).

Question 12

Increased amounts of conjugated bilirubin are found in the plasma (and urine) in:

Answer 12

Decreased excretion of bilirubin as seen in obstructive liver disease and in specific rare inherited syndromes (Rotor’s and Dubin-Johnson syndromes).

Question 13

Increased amounts of urobilinogen are found in the urine in:

Answer 13

Normal urine contains some urobilinogen.
Increased amounts of urobilinogen are found in the urine in:
* Increased bilirubin production.
* Decreased re-uptake into liver due to hepatocellular dysfunction (but not if obstruction prevents bilirubin to reach GIT).

Question 14

What are enzymes that reflect liver damage?

Answer 14

Aspartate aminotransaminase (AST) has widespread tissue distribution including liver, red blood cells, skeletal and cardiac muscle.

Alanine transaminase (ALT) is more liver-specific.

Lactate Dehydrogenase (LD or LDH) has widespread tissue distribution including liver, red blood cells, skeletal and cardiac muscle.
The LD5 isoenzyme is found in the liver and skeletal muscle only

Question 15

How can Plasma Proteins be used in the diagnosis of liver diseases?

Answer 15

Albumin is decreased in chronic liver disease, but is insensitive as an index of liver function.
Clotting factors have short half-lives, e.g. factor VII t½ = 4h. The prothrombin time (INR) and partial thromboplastin time (PTT) may be prolonged in liver disease
Immunoglobulins show a generalised increase (polyclonal) in chronic liver disease, especially cirrhosis.
* In primary biliary cirrhosis IgM is characteristically increased.
* In alcoholic cirrhosis IgA is characteristically increased
* In autoimmune chronic active hepatitis IgG is particularly increased

Question 15

What are Enzymes Reflecting Cholestasis?

Answer 15

Alkaline phosphatase (ALP) has widespread tissue distribution including liver, bone, placenta and GIT. It is released into plasma in cholestasis.

Gamma-glutamyl transferase (GGT) is more liver-specific. Serum level increased by cholestasis or chronic ingestion of alcohol, barbiturates, phenytoin and other drugs which induce the enzyme.

5’-nucleotidase (5’-NT): This enzyme is also elevated in cholestasis, especially when ALP is elevated.

Question 16

What is jaundice?
Jaundice becomes clinically visible when serum bilirubin is___

Answer 16

This is the yellow appearance of skin and sclerae due to the presence of an excessive amount of bilirubin (jaundice becomes clinically visible when serum bilirubin is >40 μmol/l).
The liver has a large reserve capacity - jaundice only appears with severe impairment of liver function

Question 16

What are the Prehepatic causes of Jaundice?

Answer 16

A. Prehepatic Jaundice (increased production of bilirubin)
Haemolytic Disorders
* Abnormal haemoglobins (e.g. sickle cell anaemia).
* RBC membrane defects (e.g. hereditary spherocytosis).
* Malaria.

Ineffective Erythropoiesis
* Megaloblastic anaemias.

Question 16

What are the intrahepatic causes of jaundice?

Answer 16

B. Intrahepatic Jaundice (decreased handling of bilirubin by the liver)
- Decreased uptake of bilirubin
- Decreased conjugation of bilirubin
- Decreased excretion of bilirubin into bile canaliculi

Defect In Uptake / Conjugation Of Bilirubin
GILBERT’S SYNDROME
CRIGGLER-NAJJAR SYNDROMES :

Defect in Excretion of Bilirubin into Bile Canaliculi
DUBIN-JOHNSON and ROTOR’S SYNDROMES :
* Benign inherited disorders.
* Increased levels of conjugated bilirubin in serum and urine.
* Due to impaired excretion

Question 17

What is acute viral hepatitis?

Answer 17

• This is a common infectious disease worldwide.
• Clinical severity varies from asymptomatic, through mild hepatitis, to severe fulminant hepatitis which can be fatal.
• It is responsible for the majority of chronic liver disease, which in turn may be associated with hepatocellular carcinoma.
• Causes are hepatitis A and B (commonest), Non-A, Non-B hepatitis (Hepatitis C, D and E viruses) EBV, CMV

Question 18

What is Biochemical Features in Hepatitis?

Answer 18

Bilirubin
increased unconjugated bilirubin throughout, and increased conjugated bilirubin especially during obstructive phase.
Urine positive for bilirubin, and urobilinogen increased due to impaired re-uptake of urobilinogen by liver.
ALT and AST : Early rise in serum transaminases reflecting hepatocyte damage. Start to rise before onset of jaundice and it may be elevated without jaundice. In massive hepatic necrosis transaminases levels may suddenly decrease (grave prognostic sign)
ALP and GGT : Not greatly elevated early. Later marked increases as intrahepatic cholestasis develops due to swelling of cells

Question 19

Causes of INTRAHEPATIC CHOLESTASIS

Answer 19

• Drugs
• Benign recurrent intrahepatic cholestasis. Precipitated by viral infections.

Question 20

Plasma proteins in hepatits

Answer 20

Albumin only slightly decreased due to long half-life. It may be normal depending on the severity
Immunoglobulins: early increase in IgM, later IgG.
Decreased prothrombin index due to impaired synthesis of clotting factors. Not restored by vitamin K.
Transient mild rise in alpha-foetoprotein during regeneration phase

Question 21

What is TOXIC HEPATITIS?

Answer 21

TOXIC HEPATITIS
The liver is the site of metabolism of most drugs. Many drugs are hepatotoxic. Some have idiosyncratic reactions, others affect all individuals. Drugs may cause either:
Toxic hepatitis (e.g. alcohol, paracetamol). Biochemical changes similar to acute viral hepatitis.

Question 22

Alcoholic Liver Disease

Answer 22

A range of liver pathology may occur in alcoholic liver disease, ranging from fatty liver, to alcoholic hepatitis, to full blown alcoholic cirrhosis.
Biochemical features include:
* raised GGT because of induction as well as cholestasis
* mild disease - few additional biochemical indicators are present
* severe disease- transaminases are elevated, especially AST (therefore the ALT/AST ratio is less than 1)
* in cirrhosis increased immunoglobulins esp. IgA

Question 23

NON-ALCOHOLIC STEATOHEPATITIS (NASH)

Answer 23

A form of chronic hepatitis which is similar histologically to alcoholic hepatitis, but which occurs in non-alcoholic patients
The pathogenesis is not yet known,
Although the cause has not yet been definitively determined, risk factors associated with the condition include:
* obesity
* Non insulin dependent diabetes mellitus (NIDDM)
* jejenal-ileal bypass
* small bowel resection and small bowel bacterial contamination
* drugs such as amiodarone, calcium channel blockers and others.

Biochemical features include:
* raised transaminases, especially ALT
* hyperlipidaemia
* NIDDM

Question 24

Causes of SPACE-OCCUPYING LESIONS OF THE LIVER

Answer 24

Primary liver cell carcinoma (hepatoma).
Marked increase in alpha-foetoprotein.
Predisposing factors:
Cirrhosis.
Previous hepatitis B infection.

Question 24

What are the types of gallstones and what causes them?
What is the presentation?

Answer 24

Cholesterol stones. The common gallstone. Predisposing factors are obesity, increasing age, female sex, diabetes, hyperlipidaemia , chronic cholecystitis ,relative deficiency of tri- and dihydroxy bile salts

Treatment: Oral chenodeoxycholic acid has been used therapeutically.

Pigment stones.
Excess (unconjugated) bilirubin production in haemolytic anaemias.

PRESENTATION:
Intermittent passage of gallstone:
Severe right upper quadrant abdominal pain (biliary colic).
Intermittent jaundice and bilirubinuria.
Intermittent elevations of ALP, GGT.
Prolonged painless obstructive jaundice.

Question 25

Features of SPACE-OCCUPYING LESIONS OF THE LIVER

Answer 25

Features:
Enlarged firm liver.
Increased ALP, GGT due to local obstruction
However jaundice is rarely present and serum bilirubin is normal or only slightly increased, since remaining normal tissue has large reserve capacity for excreting bilirubin.
AST, ALT normal/slightly increased

Question 26

What is neonatal jaundice?

Answer 26

In utero, bilirubin is transported across the placenta, conjugated and excreted by the mother’s liver. After birth the neonate must excrete the bilirubin.
Factors contributing to neonatal jaundice are increased relative RBC mass, shorter RBC lifespan, immature liver, especially in premature neonates (takes 2-4 weeks to develop fully).

Question 27

Physiological Jaundice

Answer 27

Jaundice develops on days 3-5 (never on day1).
Levels of bilirubin may reach 150 μmol/l, all unconjugated.
Usually phototherapy is all the treatment that is required.

Question 28

What is the treatment for neonatal jaundice?

Answer 28

Phototherapy - Light at 440-470 nm causes formation in skin of isomers of unconjugated bilirubin which are more soluble, excreted in urine.
Exchange transfusion required when bilirubin > 305 μmol/l (term babies) or > 200 μmol/l in premature babies or case of clinical features of kirnecturus

Question 29

What are complications of neonatal jaundice? What are the risk factors?

Answer 29

Risk of kernicterus when unconjugated bilirubin > 200 μmol/l. Risk is increased by other factors like
Level of unconjugated bilirubin.
Low albumin.
Drugs (displace bilirubin from albumin).
Acidosis (promotes dissociation of bilirubin from albumin).
Heparin administration (causes liberation of free fatty acids which displace bilirubin from albumin).
Hypoxia, hypoglycaemia, hypothermia, sepsis (increase bilirubin transport into the brain).

Question 30

Non Physiological Jaundice

Answer 30

Jaundice develops on day 1 in neonates.

Rhesus or ABO systems commonly responsible.

A few foetal RBCs cross into maternal circulation, mother makes antibodies if blood groups are incompatible. These IgGs then pass into foetal circulation, causing haemolysis of foetal RBCs.

Excessive bilirubin production is not a problem for the foetus, since it crosses placenta and is conjugated, excreted by mother’s liver.

However, bilirubin starts rising rapidly after birth. Severe haemolysis in utero causes foetal anaemia and heart failure (“hydrops foetalis”).

Inherited haemolytic disorders.

Question 31

Impaired excretion of bilirubin that has been conjugated
in hepatocytes (causing conjugated hyperbilirubinaemia) may be due to what conditions?

Answer 31

Neonatal hepatitis : Many infective agents can cause hepatitis in neonates (e.g. rubella, CMV, herpes simplex, toxoplasmosis).

Biliary atresia : Cause of biliary atresia is unclear: may be toxic degeneration of bile duct rather than a congenital malformation.
Metabolic disorders like in inborn error of metabolism explained above

TREATMENT
- Treat the underlying condition