What is the Difference Between CRP and Homocysteine

The main difference between CRP and homocysteine is that the C-reactive protein (CRP) is a substance produced by the liver in response to inflammation whereas the homocysteine is a common amino acid found in the blood. 

CRP and homocysteine are two types of substances in the blood. Their elevated levels are risk factors for different disease conditions. In fact, high levels of CRP in the blood is a risk factor for the early development of heart disease while high levels of homocysteine is a risk factor of endothelial cell injury.

Key Areas Covered 

1. What is CRP
     – Definition, Facts, Elevation
2. What is Homocysteine
     – Definition, Facts, Elevation
3. What are the Similarities Between CRP and Homocysteine
     – Outline of Common Features
4. What is the Difference Between CRP and Homocysteine
     – Comparison of Key Differences

Key Terms 

CRP (C-Reactive Protein), Endothelial Cell Injury, Heart Disease, Homocysteine, Inflammation

What is CRP 

C-reactive protein (CRP) is a ring-shaped, pentameric protein that naturally occurs in the blood. The other names for CRP are the high-sensitivity C-reactive protein (hs-CRP) and ultra-sensitive C-reactive protein (us-CRP). However, the liver produces CRP in response to factors like interleukin-6 released by adipocytes, macrophages, and T cells during inflammation. Thus, this results in the elevation of the levels of CRP in the blood. The main function of CRP is to bind to the lysophosphatidylcholine expressed on the surface of dead cells or some bacteria. This binding activates the complement system to clear up the dead cells and bacteria. 

Figure 1: CRP Structure

The elevated levels of CRP also serve as a risk factor of heart disease. Along with the other risk factors including hypertension, diabetes, elevated cholesterol levels, age, smoking, obesity, and the family history of heart diseases, CRP can cause heart disease. 

What is Homocysteine 

Homocysteine is an α-amino acid, which is not used in protein synthesis. Our body produces homocysteine from methionine. And, the main function of homocysteine is to be converted into cysteine, which is a homologous amino acid of it.  

Figure 2: Homocysteine

However, the elevated levels of homocysteine in the blood is a risk factor for endothelial cell injury and can lead to inflammation. Furthermore, the inflammation in the blood vessels can lead to atherogenesis and then Ischemic injury. That means; the elevated levels of homocysteine are a risk factor of coronary artery disease.  

Similarities Between CRP and Homocysteine 

• CRP and homocysteine are two types of substances normally found in the blood. 
• The elevated levels of these substances may lead to different clinical conditions.  

Difference Between CRP and Homocysteine 

Definition 

CRP (C-reactive protein) refers to a substance produced by the liver in response to inflammation. Homocysteine refers to an amino acid which occurs in the body as an intermediate in the metabolism of methionine and cysteine. Thus, this explains the main difference between CRP and homocysteine.

Type of Molecule 

Also, CRP is a protein while homocysteine is an amino acid.  

Structure 

Another difference between CRP and homocysteine is that the CRP is a ring-shaped pentameric protein while the homocysteine is a non-proteinogenic, α-amino acid.  

Biosynthesis 

Moreover, CRP is synthesized in the liver while homocysteine is biosynthesized from methionine. 

Function 

CRP activates the complement system while homocysteine serves as an intermediate for the biosynthesis of cysteine. Hence, this is another difference between CRP and homocysteine.

Normal Levels 

Besides, the normal levels of CRP in blood should be lower than 1.0 mg/L while the normal levels of homocysteine in blood should be 4-15 µmol/L.  

Elevated Levels 

The impact due to the elevated levels of these substances contributes to another difference between CRP and homocysteine. The elevated levels of CRP in the blood are a risk factor for the early development of heart disease while the elevated levels of homocysteine are a risk factor of endothelial cell injury. 

Conclusion 

CRP is a serum protein produced by the liver in response to the inflammation. It is important in the activation of the complement system. On the other hand, homocysteine is an amino acid that serves as an intermediate in the synthesis of cysteine. Therefore, the main difference between CRP and homocysteine is the structure, function, and clinical implications.  Furthermore, elevated levels of both these substances can cause clinical problems. 

References:

1. Stöppler, Melissa Conrad. “C-Reactive Protein Normal Ranges, Elevated Treatment & Symptoms.” MedicineNet, Available Here
2. Davis, Charles Patrick. “Homocysteine (Normal and Elevated) Levels: Causes & Treatments.” MedicineNet, Available Here

Image Courtesy:

1. “PDB 1b09 EBI” By Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute – http://www.ebi.ac.uk/pdbe-srv/view/images/entry/1b09600.png, displayed on http://www.ebi.ac.uk/pdbe-srv/view/entry/1b09/summary (Public Domain) via Commons Wikimedia  
2. “Homocysteine racemic” By Edgar181 – Own work (Public Domain) via Commons Wikimedia