Metabolism of bilirubin and approach to hyperbilirubinemia

1. METABOLISM OF
BILIRUBIN AND
APPROACH TO A
PATIENT WITH
HYPERBILIRUBINEMIA

2. CONTENTS
BILIRUBIN
• Production of bilirubin.
• Sources
• Metabolism
• Fate of bilirubin conjugates
• Delta bilirubin
HYPERBILIRUBINEMIA
• Introduction
• Evaluation of patient with jaundice
• Causes of unconjugated hyperbilirubinemia
• Causes of conjugated hyperbilirubinemia
• Lft patterns in hepatobiliary disease

3. PRODUCTION OF BILIRUBIN
• tetrapyrrole pigment.
• breakdown product of heme.
• amount produced each day - 4 mg/kg body weight
• The formation of bilirubin occurs in reticuloendothelial cells,
primarily in the spleen and liver.

4. SOURCES
ERYTHROID
• 80–85% from senescent red blood cells.
• prematurely destroyed erythroid cells in bone marrow
NON ERYTHROID
• hemoproteins such as myoglobin and cytochromes found in tissues
throughout the body

5. • Bilirubin formed in the reticuloendothelial cells is
insoluble in water due to tight internal hydrogen bonding
between the water-soluble moieties of bilirubin—that is, the
bonding of the propionic acid carboxyl groups of one
dipyrrolic half of the molecule with the imino and lactam
groups of the opposite half. This configuration blocks
solvent access to the polar residues of bilirubin and places
the hydrophobic residues on the outside.
• Bilirubin must be solubilized to be transported in blood,.
Solubilization is accomplished by the reversible,
noncovalent binding of bilirubin to albumin.

7. • Unconjugated bilirubin bound to albumin is transported to the liver.
• There, the bilirubin is taken up by hepatocytes via carrier mediated
membrane transport.
• After entering the hepatocyte, unconjugated bilirubin is bound in the
cytosol to proteins in the glutathione-S transferase superfamily.
• These proteins reduce efflux of bilirubin back into the serum and present
the bilirubin for conjugation.
• In the endoplasmic reticulum, bilirubin is made aqueous soluble by
conjugation to glucuronic acid, a process that disrupts the
hydrophobic internal hydrogen bonds and yields bilirubin
monoglucuronide and diglucuronide. The conjugation is catalyzed by
bilirubin uridine diphosphateglucuronosyl transferase (UDPGT).

8. FATE OF HYDROPHILIC BILIRUBIN CONJUGATES
• diffusion from the endoplasmic reticulum to the canalicular
membrane, where bilirubin monoglucuronide and
diglucuronide are
• actively transported into canalicular bile by multidrug
resistance–associated protein 2 (MRP2).
• A portion of bilirubin glucuronides is transported into the
sinusoids and portal circulation by MRP3 and is subjected
to reuptake into the hepatocyte by the sinusoidal organic
anion transport protein 1B1 (OATP1B1) and OATP1B3.

10. The conjugated bilirubin passes unchanged through the
proximal small bowel and not reabsorbed by the
intestinal mucosa due to its hydrophilicity and increased
molecular size.
When the conjugated bilirubin reaches the distal ileum and
colon
-hydrolyzed to unconjugated bilirubin by bacterial β-
glucuronidases.
-reduced by normal gut bacteria to form a group of
colorless tetrapyrroles called urobilinogen.

11. • 80–90% of these products
are excreted in feces,
either unchanged or
oxidized to orange
derivatives called urobilins.
• 10–20% of the
urobilinogens undergo
enterohepatic cycling.
• A small fraction (usually
<3mg/dl) is excreted in
urine.

12. DELTA BILIRUBIN / DELTA FRACTION/
BILIPROTEIN
• This albumin-linked fraction of conjugated bilirubin represents an important
fraction of total serum bilirubin in patients with cholestasis and hepatobiliary
disorders. The delta bilirubin is formed in serum when hepatic excretion of
bilirubin glucuronides is impaired and the glucuronides accumulate in serum.
• the clearance rate of delta bilirubin from serum approximates the half-life of
albumin (12–14 days) rather than the short half-life of bilirubin (about 4 h).
• The prolonged half-life of albumin-bound conjugated bilirubin accounts for
• - some patients with conjugated hyperbilirubinemia do not exhibit bilirubinuria
during the recovery phase of their disease because the delta bilirubin, although
conjugated, is covalently bound to albumin and therefore not filtered by the renal
glomeruli, and
• -that the elevated serum bilirubin level declines more slowly than expected in
some patients who otherwise appear to be recovering satisfactorily.

13. HYPER
BILIRUBINEMIA

14. INTRODUCTION
Hyperbilirubinemia is a condition in which there is a build up of bilirubin in the blood,
causing yellow discoloration of the eyes and skin, called jaundice.
• sign of
- either liver disease or,
- a hemolytic disorder or
- disorder of bilirubin metabolism
• the presence of scleral icterus indicates a serum bilirubin level of at least 3 mg/dL.
• The differential diagnosis for yellowing of the skin.(In addition to jaundice)includes
• Carotenoderma- associated with diabetes, hypothyroidism, and anorexia nervosa, but most
commonly, it is caused by the ingestion of an excessive amounts of carotene.
• Drugs- quinacrine, sunitinib, and sorafenib
• excessive exposure to phenols.
• In jaundice, the yellow coloration of the skin is uniformly distributed over the body,
whereas in carotenoderma, the pigment is concentrated on the palms, soles, forehead,
and nasolabial folds. Carotenoderma can be distinguished from jaundice by the sparing of
the sclerae.

16. Initial Evaluation: History
• Jaundice, acholic stools, tea-colored urine
• Fever/chills, RUQ pain (cholangitis)
Could lead to life-threatening septic shock
• Reasons to have hepatitis or cirrhosis?
Alcohol, Viral, risk factors for viral hepatitis
• Exposure to toxins or offending drugs
• Inherited disorders or hemolytic conditions
• Recent blood transfusions or blood loss?
• Is patient septic or on TPN?

17. Initial Evaluation: Physical Exam
• Signs of end stage liver disease (cirrhosis)
Ascites, splenomegaly, spider angiomata, and
gynecomastia
• Jaundice evident first underneath the tongue, also
evident in sclerae or skin

18. UNCONJUGATED HYPERBILIRUBINEMIA
1. INCREASED BILIRUBIN PRODUCTION
2. DECREASED HEPATIC BILIRUBIN CLEARANCE
3. HEREDITARY DEFECTS IN BILIRUBIN CONJUGATION
1. INCREASED BILIRUBIN PRODUCTION
- Hemolysis leads to unconjugated hyperbilirubinemia;
hemolysis alone cannot result in a sustained
hyperbilirubinemia of more than 4 mg/dL. Higher values
imply concomitant hepatic dysfunction.

19. UNCONJUGATED HYPERBILIRUBINEMIA
- Ineffective Erythropoiesis
During erythroid maturation, small amounts of hemoglobin may be lost at
the time of nuclear extrusion, and a fraction of developing erythroid cells is
destroyed within the marrow. These normally account for a small
proportion of bilirubin production.
In thalassemia major, megaloblastic anemias due to folate or vitamin B12
deficiency, congenital erythropoietic porphyria, lead poisoning, the
fraction of total bilirubin production derived from ineffective
erythropoiesis is increased,.
Miscellaneous Degradation of the hemoglobin of extravascular collections
of erythrocytes, such as those seen in massive tissue infarctions or large
hematomas, may lead transiently to unconjugated hyperbilirubinemia

20. 2. DECREASED HEPATIC BILIRUBIN CLEARANCE
Decreased Hepatic Uptake
Gilbert’s syndrome
Drugs- flavaspidic acid, novobiocin, and rifampin cholecystographic contrast
agents, have been reported to inhibit bilirubin uptake. Resolves with
cessation of the medication.
Impaired Conjugation
• PHYSIOLOGIC NEONATAL JAUNDICE - hepatic physiologic processes
are incompletely developed at birth. Levels of UGT1A1 are low, Since
the intestinal flora that convert bilirubin to urobilinogen are also
undeveloped, an enterohepatic circulation of unconjugated bilirubin
ensues.

21. As a consequence, most neonates develop mild unconjugated
hyperbilirubinemia between days 2 and 5 after birth.
ACQUIRED CONJUGATION DEFECTS
- advanced hepatitis or cirrhosis.
-drugs, including pregnanediol, novobiocin, chloramphenicol, gentamicin,
and atazanavir,
-breast milk jaundice

22. 3. HEREDITARY DEFECTS IN BILIRUBIN
CONJUGATION

23. MIXED OR PREDOMINANTLY CONJUGATED
HYPERBILIRUBINEMIA

27. Inheritable Disorders of Bile Canalicular
Function

29. 8YR old child presents with jaundice and easy fatiguability. He had h/o ear
infection which was treated with amoxyclav. Investigations are as follows :
Hb – 8mg/dl
Total Bilirubin – 3.5mg/dl
Direct bilirubin – 1 mg/dl
ALT – 45 IU/L
AST- 42 IU/L
Other LFT – normal
USG – shows gall stones.
a) Drug induced hepatitis
b)Hemolytic jaundice
c) Obstructive jaundice
d) Gilbert syndrome.

31. Q. 2 wk old baby presented with yellowish
discolouration of skin. Investigations revealed
markedly elevated direct bilirubin levels. Which of
the following should be suspected?
a) Biliary atresia
b)Physiological jaundice
c)Breast milk jaundice
d)Hemolytic disease of newborn

32. Q) Investigations performed in a pt with recurrent
jaundice gave the following results. What is the
possible cause of jaundice in this case?
total bilirubiin : 4mg/dl
Urine bilirubin : +
a) Hemolytic anemia
b)Gilbert syndrome
c)Criggler najjar syndrome
d)Dubin johnson syndrome

33. THANK YOU