Biochemistry, Ceruloplasmin

Article Author:
Michael Lopez
Article Author:
Amor Royer
Article Editor:
Niraj Shah
Updated:
5/5/2020 11:21:11 AM
PubMed Link:
Biochemistry, Ceruloplasmin

Introduction

Ceruloplasmin is a serum ferroxidase responsible for 90% of copper transport. It is well known for its role in the pathogenesis of Wilson disease and iron metabolism.[1] Also, ceruloplasmin is a positive acute-phase reactant, meaning its levels will increase in inflammatory conditions or cell injury.[2]

Fundamentals

Ceruloplasmin production occurs in the liver and is a ferroxidase enzyme that is encoded by the CP gene in humans.[3] Liver hepatocytes mostly synthesize ceruloplasmin. In the liver, P-type ATPase (ATPase 7B) enzymes are necessary to incorporate copper into apo-ceruloplasmin.[4] Ceruloplasmin is then released into the bloodstream to transport proper to distal sites and to complete its functions in other metabolic processes, namely iron metabolism. A solution of ceruloplasmin is blue, and excess in serum may give the serum a greenish hue. Each ceruloplasmin molecule can contain 6 to 8 copper atoms.[5] 

Issues of Concern

Ceruloplasmin is not a routine value measured in standard labs. Ceruloplasmin is an acute phase reactant and may become elevated when someone has any form of trauma, tissue damage, infection, or inflammation. It bears mention that ceruloplasmin may be high in states of high estrogen and progesterone, which means pregnant women or women on oral contraceptives may have high levels of ceruloplasmin.[2] Many medications, most notably the anti-seizure drugs (e.g., valproic acid), are also known to increase levels of ceruloplasmin.  As stated before, ceruloplasmin is not routinely measured, but the following symptoms may prompt ordering of ceruloplasmin levels: 

  • Anemia
  • Ataxia
  • Nausea and abdominal pain
  • Neuropathy
  • Jaundice
  • Fatigue
  • Behavioral changes
  • Tremors
  • Difficulty walking or swallowing
  • Dystonia

Cellular

It is synthesized primarily in the liver parenchymal cells, with small amounts coming from macrophages and lymphocytes.[6] The peptide chain is synthesized then copper is added from an intracellular ATPase.[7] Copper is essential for the normal folding of ceruloplasmin as well as for the normal oligosaccharide attachment. Much of the apo-ceruloplasmin, which does not contain copper or the ATPase, undergoes intracellular degradation, although a small portion will reach circulation but has a short half-life of 4 to 5 days. 

Molecular

Ceruloplasmin has a molecular weight of 132kDa, and has a polypeptide chain of 1046 amino acids and three asparagine-linked oligosaccharides, with a total carbohydrate content of 10%. Size and charge of the molecule depend on glycosylation of the molecule, the number of copper atoms, peptide chain variations, and polymerization. Ceruloplasmin is highly prone to proteolysis. The structure of ceruloplasmin can be studied by electron paramagnetic resonance spectroscopy.

Function

The molecule is a catalyst for redox reactions in plasma. It can oxidize iron from ferrous (2+) to ferric iron (3+), and this assists in the binding of iron to transferrin. It is also thought to be involved in controlling membrane lipid oxidation. In the presence of superoxide, ceruloplasmin promotes LDL oxidation and may contribute to atherosclerosis.

Ceruloplasmin has a limited role in copper transport to the tissues. Absorbed copper is transported to the liver bound to albumin via the portal system. The liver is the key organ in copper homeostasis, and more than 90% of the copper exported from the liver is in the form of ceruloplasmin.

Mechanism

Neurological disorders in hereditary ceruloplasmin deficiency may be caused by disordered iron transport in the brain. Ceruloplasmin has a limited role in plasma copper transport to tissues. Albumin and transcuprein appear to be the other major copper transport proteins, especially immediately post gastrointestinal absorption. 

Testing

Ceruloplasmin measurement is via a blood test, which often occurs by analyzing a serum sample with immunoassays, immunoturbidimetry, or immunonephelometry. The sample needs to be spun and separated as soon as the laboratory receives it and assayed promptly. The samples may be stored at 4 degrees Celius for up to three days or for longer at -70 degrees Celsius. The serum test is often part of the workup when there is suspicion of Wilson disease and is commonly ordered along with urine copper levels. Several factors, including diet, hormone levels, and other genetic disorders, may influence the resulting levels of ceruloplasmin in the urine and serum.

Deficiency States 

Lower-than-normal ceruloplasmin levels may indicate the following: Wilson disease, Menke disease, copper deficiency, aceruloplasminemia, or in general states of low protein intake (e.g., malnutrition)

Excess 

Greater-than-normal ceruloplasmin levels may indicate or present in copper toxicity/zinc deficiency, pregnancy, oral contraceptive use, lymphoma, acute and chronic inflammation, rheumatoid arthritis, angina, Alzheimer disease, schizophrenia, obsessive-compulsive disorder 

Reference intervals:(adapted from Tietz Textbook of Clinical Chemistry and Molecular Diagnostics by Carl A Burtis et al.)

Age/Interval(mg/L)

  • Cord(term): 50 to 330
  • Birth to 4 months: 150 to 560
  • 5 to 6 months: 260 to 830
  • 7 to 36 months: 310 to 900
  • 6 to 12 years: 250 to 450

Age/Male/Female

  • 13 to 19 years: 150 to 370/220 to 500
  • Adult: 220 to 400/250 to 600 (no oral contraceptives)
  • Adult: 270 to 660 (on oral contraceptives, estrogens)
  • Adult: 300 to 1200 (pregnant)

When it comes to serum ceruloplasmin testing, only those with low serum ceruloplasmin, low serum copper, and high urine copper meet the criteria for Wilson disease. There have been patients diagnosed with Wilson's disease, exhibiting normal ceruloplasmin levels. When urine and serum concentrations of both copper and ceruloplasmin are low, then the patient is simply suffering from a copper deficiency. Anything interfering with the body's ability to metabolize copper may also affect the serum ceruloplasmin levels.

Pathophysiology

Ceruloplasmin is undetectable before 20 weeks of gestation. Concentrations gradually rise to 25 to 40% of normal adult concentrations and by six months are close to adult concentrations

Special Situations:

  • There have been reports of inherited aceruloplasminemia in several families and is a genetic cause for ceruloplasmin deficiency; these patients have neurodegeneration and iron deposition in the brain.[8] Concerning aceruloplasminemia, a diagnosis of aceruloplasminemia could be suspected based upon a biochemical profile showing very low to absent ceruloplasmin in serum, high ferritin, low copper, low iron, microcytic anemia refractory to iron supplementation, and characteristic imaging features. Homozygous cases have characteristic imaging features with marked hypointensity of the liver, basal ganglia nuclei, thalami, dentate nuclei, and cerebral/cerebellar cortices on T2 MRI. MRI of heterozygous cases may reveal cerebellar atrophy without hypointensity of the basal ganglia.[9] 
  • Menke's disease is an X-linked recessive disorder caused by a mutation in the ATP7A protein. With this mutation, copper cannot be transported out of the GI tract, and therefore copper is not available to the liver, which causes low ceruloplasmin levels. The patients present in infancy and have sparse, brittle, and kinky hair, growth retardation and neurologic degradation and death in the first few years of life if untreated.[10]
  • Wilson's disease results from an autosomal recessive mutation in the ATP7B protein. Mutations in ATP7B (located on chromosome 13) lead to Wilson's disease. ATP7B is an efflux transporter in the liver, but it is also essential in the Trans-Golgi Network for the transfer of copper for metalation of ceruloplasmin and biliary copper excretion.[11] The point mutation H1069Q is the most common ATP7B mutation in patients from Central, Eastern, and Northern Europe, and 50 to 80% of Wilson disease patients from these countries carry at least one H1069Q allele.[12] Mutations resulting in completely absent or non-functional ATP7B protein activity are associated with early-onset, typically hepatic, severe Wilson's disease; these mutations are comparatively rare.[13] It is characterized by hepatolenticular degeneration due to copper deposition in organs, including the basal ganglia, cornea, and liver. In Wilson's disease, ceruloplasmin levels will usually be low, but urinary excretion of copper will be high. Liver biopsy results will show high copper content. Clinically, the presence of a dark ring around the iris is suggestive of a diagnosis of Wilson disease. This sign is known as a Kayser-Fleischer ring.[14]

Clinical Significance

Treatment for aceruloplasmin and Wilson disease:

Treatment for aceruloplasminemia mostly falls to chelation therapy and increasing serum ceruloplasmin. FFP (which contains ceruloplasmin) combined IV desferrioxamine is effective in decreasing iron content in the liver. Repetitive FFP treatment can improve neurologic signs/symptoms.

Treatment options for Wilson disease include chelation therapy (D-penicillamine, trientine, and tetrathiomolybdate) and/or zinc salts. Medical therapy is continued life long as copper accumulation is not manageable with dietary restriction alone. It is important to note that there may be an associated paradoxical worsening of neurological status after initiation of chelation therapy. While this is not fully understood, studies suggest that increased mobilization of free copper by chelator therapy may lead to acute worsening upon initiation of treatment.[13]

Complications:

Diabetes mellitus, ataxia, dystonia, Parkinsonism, psychiatric problems (mostly mood disorders), cardiac disease, thyroid dyscrasia, anemia, and liver damage are common complications shared by both Wilson disease and aceruloplasminemia. Amenorrhea and frequent abortions may be complications of copper toxicity that may affect fertility. Antipsychotic drugs are applied in severe mania and for the treatment of psychotic symptoms. In Wilson's disease, antipsychotics pose an increased risk of neurological deterioration and hepatic injury. As such, antipsychotics with low EPS risk, such as clozapine or quetiapine, should be used.[15]

Enhancing Healthcare Team Outcomes:

Surveillance should include yearly glucose tolerance tests starting at age 15 or age of diagnosis if, after 15 years old, to monitor for the inception of diabetes mellitus. Regular eye exams should also be a consideration as retinopathy is a prominent feature in aceruloplasminemia and Wilson disease. Yearly EKG, evaluation of thyroid and liver function in addition to CBC starting at the time of diagnosis, should be performed to monitor for other potential complications. Blood transfusions should be approached cautiously as the increased iron load may be difficult for patients with these disorders.

In patients with Wilson disease, it is a strong recommendation to perform familial screening. The American Association for Study of Liver Diseases and European Association for Study of Liver both separately recommend screening first-degree relatives of the affected individuals, suggesting siblings or offspring only.[16]

While most patients with Wilson disease who become pregnant have successful pregnancies, a discussion is necessary about potential side effects of anti-copper therapy as all available anti-copper drugs can pass into breast                                                      

Ceruloplasmin Interpretation Adapted from Labtestsonline [See exhibit 2]

Wilson's Disease [17]:

Wilson's disease presents between ages 5 to 35.

The clinical presentation may include:

  • Hepatolenticular degeneration
  • Kayser-Fleischer rings
  • Parkinsonism
  • Ataxia
  • Personality changes
  • Depression
  • Psychosis
  • Acute liver failure
  • Chronic liver failure
  • Cirrhosis 
  • Renal issues (renal tubular acidosis with aminoaciduria)
  • Secondary Hemolysis is less common
  • Most patients with Wilson disease have low ceruloplasmin levels

Treatment may include: 

  • Penicillamine
  • Trientine
  • Zinc 


  • Contributed by Dr. Ravindra Sirkar
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    • Image 11201 Not availableImage 11201 Not available
      Contributed by Dr. Ravindra Sirkar

  • Contributed by Michael Lopez, BS
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      Contributed by Michael Lopez, BS

References

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