TABLE OF CONTENTS

Title Page    –         –         –         –         –         –         –         –         –         i

Certification –         –         –         –         –         –         –         –         –         ii

Dedication   –         –         –         –         –         –         –         –         –         iii

Acknowledgements         –         –         –         –         –         –         –         iv

Table of Contents  –         –         –         –         –         –         –         –         v

CHAPTER ONE: INTRODUCTION        –         –         –         –         1

CHAPTER TWO: LIVER BIOMAKERS –         –         –         –         6

2.1     Bilirubin      –         –         –         –         –         –         –         –         7

2.2     Conjugated Bilirubin       –         –         –         –         –         –         14

2.3     Unconjugated Bilirubin   –         –         –         –         –         –         19

2.4     Total Bilirubin       –         –         –         –         –         –         –         22

2.5     Structure of Bilirubin       –         –         –         –         –         –         24

2.6     Biochemistry and Metabolism of Bilirubin    –         –         –         27

2.7     Health Benefits of Bilirubin       –         –         –         –         –         29

2.8     Function of Bilirubin       –         –         –         –         –         –         31

CHAPTER THREE: CLINICAL SIGNIFICANCE OF BILIRUBIN IN DISEASE DIAGNOSIS     –         –         –         –         –         –         –          35

3.1     Clinical Significance of Bilirubin in Diagnosis of liver disease           –         –         –         –         –         –         –         38

3.2     Clinical significance of bilirubin in diagnosis of cardiovascular disease         –         –         –         –         –         –         –         –         41

3.3     Normal blood level of bilirubin –         –         –         –         –         42

CHAPTER FOUR: SUMMARY AND CONCLUSION

4.1     Summary     –         –         –         –         –         –         –         –         47

4.2     Conclusion  –         –         –         –         –         –         –         –         48

References

CHAPTER ONE: INTRODUCTION

Bilirubin (BR) is a red-orange compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body’s clearance of waste products that arise from the destruction of aged or abnormal red blood cells (Braunstein, 2019). In the first step of bilirubin synthesis, the heme molecule is stripped from the hemoglobin molecule. Heme then passes through various processes of porphyrin catabolism, which varies according to the region of the body in which the breakdown occurs. For example, the molecules excreted in the urine differ from those in the feces. The production of biliverdin from heme is the first major step in the catabolic pathway, after which the enzyme biliverdin reductase performs the second step, producing bilirubin from biliverdin (Boron, 2015). Ultimately, bilirubin in is  broken down within the  body, and  its metabolites  excreted through bile and urine; elevated levels may indicate certain diseases. It is responsible for the yellow color of healing bruises and  the  yellow discoloration in jaundice.  Its breakdown products, such as stercobilin, cause the brown color of feces. A different breakdown product, urobilin, is the main component of the straw-yellow color in urine. Although bilirubin is usually found in animals rather than plants, at least one plant species, Strelitzia nicolai, is known to contain the pigment.

Bilirubin is important metabolite of heme (ferroprotoporphyrin ix), a coordination complex that serves to coordinate iron in various protein.

It is a potentially toxic substance. However, the body has developed mechanisms for its safe detoxification and disposition. Bilirubin and its metabolites also provide the distinctive yellow colour to bile and stool and a lesser degree, urine (Shen et al., 2020). Bilirubin is an orange yellow pigment of bile that results from the degradation of various heme-containing proteins, especially from hemoglobin catabolism. Heme is broken down into biliverdin, which is converted into unconjugated or indirect bilirubin (UCB). UCB is water-insoluble and enters circulation bound to albumin. In the liver, glucuronic acid is added to UCB (conjugation) to render it into bile or recirculate back to the bloodstream, where it is filtrated by the kidneys and excreted through urine (Cappellini et al., 2019). Elevation of plasma bilirubin levels is a frequent finding both in primary and hospital care. All liver lesions induce a decrease in the hepatocyte cell count, which may cause hyperbiliru bulimia (Dufour et al., 2020). Hyperbilirubulimia can originate from an alteration in any stage of bilirubin metabolism; excess production, impaired liver uptake, conjugation defects, or biliary excretion defects (Fevery, 2019). Bilirubin is a well-established marker that is routinely included in biochemical tests for patients with liver dysfunction or any other condition. However, bilirubin is not a sensitive or specific maker of liver function, so a careful interpretation of test results is necessary for accurate diagnosis. Therefore, alterations in bilirubin concentrations should be assessed in relation to patient anamnesis, the extent of the alteration, and the pattern of concurrent biochemical alterations (Vitek, 2019).

Formation of Bilirubin

Bilirubin is derived from two main sources, 80% of bilirubin is mode from the breakdown of hemoglobin in senescent red blood cells, and prematurely destroyed erythroid cells in bone marrow. The remainder originates from the turnover of various heme-containing proteins found in other tissues, primarily the liver and muscles. These proteins include myoghosin, cytochromes, catalase, peroxidase and tryptophan pyrrolase (Ngashengva et al., 2019). About 4kg body weight of bilirubin is produced daily. Bilirubin is form from the breakdown of heme, which is derived from the degradation of red blood cells.

Cellular Heme Metabolism

Heme is a ring of four pyrroles joined by carton bridges and a central iron atom. Bilirubin is generated by a two-stage sequential catalytic degradation reaction that primarily takes place in the cells of the reticuloendothelial system, notably the spleen. Other cells include phagocytes and the kupffer cells of the liver. Heme is taken up into these cells take up the heme, and enzyme heme oxygenase acts on them. The enzyme liberates the chelated iron by catalyzing the oxidation of the alpha carbon bridge. This reaction produces an equlmolar amount of carbon monoxide which excreted by the lungs and leads to the formation of the green pigment biliverdin. This green pigment is acted upon further by the nicotinamide adenine dinucleotide phosphate (NADPH) dependent enzyme, biliverdin reductase. This process releases an orange-yellow pigment known as bilirubin. Heme oxygenase as mentioned above is present in high concentrations in the kupffer cells of the liver and the cells of the reticuloendothelial system. Heme oxygenase is the rate-limiting factor in bilirubin production.