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Aspartate Transaminase (AST)

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Read the article to know the importance, specificity, structure, and assessment of the enzyme pivotal to general health - aspartate transaminase or SGOT.

Medically reviewed by

Dr. Jagdish Singh

Published At February 9, 2022
Reviewed AtMarch 31, 2023

Abstract:

Read the article to know the importance, specificity, structure, and assessment of the enzyme pivotal to general health - aspartate transaminase or SGOT.

What Is Aspartate Transaminase?

Aspartate transaminase (AST) also known by other names in medical terminology as glutamic oxaloacetate transaminase (GOT) or serum glutamic-oxaloacetate transaminase (SGOT) is an important clinical biomarker for liver function and liver disease as well as a crucial part of the amino acid metabolism in our body. This enzyme is an important catalyst biochemically that aids the transfer reversibly between aspartate and glutamate and has a half-life of approximately around 17 hours.

The sinusoidal cells of the liver clear the enzyme. Serum AST, as well as Serum ALT (AST/ALT ratio), is assessed commonly by physicians through blood tests for detecting any related liver inflammation, infection, injury, or disease. The reduction in this enzyme is also associated with inhibition of vitamin B6, more prevalently observed in patients suffering from gastrointestinal injuries and diseases or disorders resulting from nutritional deficiencies. The AST enzyme is present in most of the tissues except in the human bone. The normal range of AST level is usually from 8 to 40 IU/L in males and from 6 to 34 IU/L in females.

What Is the Physiology of Aspartate Transaminase?

AST activity is not only higher but also markedly increased in the liver, skeletal, and cardiac muscles in not only humans but most of the animal species as well. AST is located within the cytosol but more pronounced within the cell organelle mitochondria. AST has also been found in a number of microorganisms like E.coli and T.Thermopolis. GOT1 (Glutamic-Oxaloacetic Transaminase 1) or cAST (cytosolic AST) is the enzyme in the cytosol or cytosolic enzyme derived in the heart muscle and red blood cells or erythrocytes. The GOT2 (Glutamic-Oxaloacetic Transaminase 2) or mAST is the enzyme present in liver tissues.

The GOT1 and GOT2 or the cAST and mAST are rather isoenzymes found commonly in us by gene duplication. An increase in serum AST along with an elevated creatine kinase enzyme activity is suggestive of a long-standing liver issue more commonly a liver injury. As the diagnostic sensitivity for just AST to estimate liver function is less, organ-specific enzymes like creatine kinase and sorbitol dehydrogenase can differentiate between hepatocellular and myocyte injuries better and are often recommended by the physician for an accurate diagnosis of cellular damage. Sorbitol dehydrogenase helps in hepatocellular injury differentiation and creatine kinase indicates myocyte injuries.

AST is also found in erythrocytes or red blood cells, hence in the laboratory analysis erythrocyte lysate can be added to increase the activity of AST according to research. Also, the serum activity of AST is considerably more stable at room temperature, frozen temperatures, and also refrigeration enhances its availability as a ready biomarker for clinical analysis of the patient profile and for screening purposes compared to sorbitol dehydrogenase and creatine kinase.

What Is the Structure of AST?

Through the method of X-ray crystallography, the structure of aspartate transaminase gives us an insight into the dimeric or two specific subunits or unit identical structures from the cytosol of species like E.Coli. The molecular weight of aspartate transaminase or AST is around 43-47 kD. The secondary structure of this enzyme is composed of alpha helices surrounding a centrally containing beta element or sheet. The enzyme specificity is by the active sites within it that are the Arg 386 and Arg 292 complexes (Arginine residues).

What Do AST Concentrations Indicate?

The highest concentrations are usually found in the liver tissues and the skeletal muscles. In exudates, transudates, and even in cerebrospinal fluid especially prove to be useful biomarkers for assessing cellular damage. Of which, AST analysis is crucial. Though concentrations are significantly lower in urine, AST levels are unimportant for renal assessment as such. Hence AST assessment is an important biomarker that needs to be correlated by the physician not just to estimate liver functions (though even liver functions cannot be completely correlated with an increased transaminase level) but also for these accessory vitamins, nutrients, cellular damage, and gastrointestinal issues.

It is essential for most physicians and patients to realize that an elevated AST level might be a source of hepatic injury, hepatic-related trauma, or causative rather than suggesting liver disease, so it is not considered entirely accurate or dependable for the same reason. Hence the reason behind the physician suggesting an aminotransferase test is to assess cell injury.

An increased AST level may be useful in prior detection of the following conditions which may be proving a source of elevation:

  • Hepatitis.

  • Myocardial infarction.

  • Hemolytic anemias.

  • Musculoskeletal disorders.

  • Genetic or metabolic liver disorders.

  • Cholestasis.

  • Chronic hepatitis (viral or autoimmune hepatitis).

  • Extrahepatic injuries.

An elevated AST level followed by a decline or reduction within 48 to 72 hours of retesting (usually that occurs once the source of hepatic obstruction has been relieved) indicates acute biliary obstruction.

A rapidly decreased or declined AST level is usually indicative of:

  • Coagulopathies (that may be chronic or may worsen untreated over time).

  • Acute liver failure.

AST Elevation in Periodontal Disease:

According to research, the estimate of biomarkers in our saliva would give us an understanding of the diagnosis of periodontal disease. Clinically and as per randomized control trials, a positive correlation has been observed in patients suffering from dental and periodontal disease with concentrated AST levels in gingival crevicular fluid or GCF that can help distinguish between healthy and diseased periodontium.

Apart from an increased AST in saliva, other enzymes like elastase, collagenase, and beta-glucuronidase, alkaline phosphatase is also indicative of periodontal pathogenesis. From a pathologic perspective, the dental surgeon or the oral surgeon diagnose periodontal disease by two major clinical parameters i.e. the probing depth and attachment loss. Radiographically through IOPA (intraoral periapical radiograph) and OPG (orthopantomogram) methods, alveolar bone loss can also be estimated.

However, these traditional diagnostic methods cannot measure or quantify the exact extent of periodontal disease. This is where the biomarker detection helps in quantification and also study the activity of a microbial organism in the saliva and also several immunologic markers as well. Salivary-based oral diagnostic criteria are now being explored to replace the traditional gold standard approach of physical examination by the dentist and are indeed promising to quantify and estimate the extent of periodontal disease or /periodontitis (gum disease and bone loss).

Conclusion:

To conclude, Aspartate transaminase is not an accurate marker to indicate specific liver disease but an elevated level or a rise in AST may be indicative of associated systemic disease pertaining to the liver, gastrointestinal, heart and periodontal disease and hence would be useful for the physician to detect the underlying cause.

Frequently Asked Questions

1.

What Is the Function of Aspartate Transaminase?

Aspartate transaminase is an important enzyme in aminoacid metabolism. It is a transaminase enzyme that catalyzes the conversion of aspartate and alpha-ketoglutarate to oxaloacetate and glutamate.

2.

What Are the Normal Levels of AST?

AST (aspartate aminotransferase) is also known as serum glutamic oxaloacetic transaminase. The normal range of values is 5 to 40 units per liter of serum.

3.

At What Levels of AST Does Liver Damage Occur?

The range of AST can vary slightly. But high levels indicate liver damage or injury due to different conditions that are two to three times the upper limit. In some liver diseases, this value can be fifty times higher than the upper limit, and the high levels are described as deranged. The relationship or ratio between ALT and AST can provide more valuable clues on whether the infection is acute or chronic.

4.

How to Test for Aspartate Transaminase?

The aspartate aminotransferase test is a blood test that checks for liver damage. Injury to the liver results in the release of AST into the blood. This test is mainly done and other tests to diagnose and monitor liver disease.

5.

How Is Aspartate Produced in the Body?

Aspartate is most frequently synthesized through the transamination of oxaloacetate. An aminotransferase enzyme aspartate aminotransferase facilitates the biosynthesis of aspartate.

6.

How Does Aspartate Transaminase Differ From Alanine Transaminase?

Aspartate transaminase is found in the liver, brain, pancreas, heart, kidneys, lungs, and skeletal muscles. Alanine transaminase is mainly found in the liver. It helps convert proteins into energy for the liver cells. AST helps metabolize amino acids.

7.

What happens if AST levels are high?

Increased levels of AST in the blood may be due to hepatitis, cirrhosis, mononucleosis, or other liver diseases. Sometimes, it can be due to heart problems or pancreatitis. The high levels may also be due to age, gender, diet, and types of medicine.

8.

What Is AST in Laboratory Blood Test Reports?

AST is often included in a routine blood screening. It is a test for aspartate aminotransferase, which is mostly found in the liver and muscles. When there is liver damage, the AST levels in the blood get elevated, which can diagnose liver damage or disease.

9.

What Is the Etiology for Low AST or ALT?

Low AST or ALT is not generally a cause of concern. But, sometimes, they may indicate some underlying medical condition such as vitamin B6 deficiency or chronic kidney disease. Factors that deplete B6 like smoking and alcoholism can also decrease ALT levels.

10.

How to Treat High AST Levels?

Depending on the liver damage, the doctor will recommend a treatment plan. The treatment for elevated liver enzymes will involve managing the underlying condition causing the increased levels. This will include lifestyle changes like losing weight, exercising, eating a balanced diet, reducing stress levels, avoiding alcohol, etc.
Dr. Jagdish Singh
Dr. Jagdish Singh

Medical Gastroenterology

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