Transaminases, also known as aminotransferases, are enzymes that play a crucial role in metabolic processes in the body. Two of the most well-known transaminases are alanine transaminase (ALT) and aspartate transaminase (AST).

These enzymes are primarily found in the liver but can also be present in other organs, such as the heart and skeletal muscles. Elevated levels of transaminases in the blood can indicate liver damage or disease, making them important markers for diagnosing and monitoring liver health.

Structure and Function of Transaminases

Transaminases are a group of enzymes that catalyze the transfer of an amino group from an amino acid to a keto acid, thereby producing a new amino acid and a new keto acid.

This process is essential for various metabolic pathways, including the synthesis of non-essential amino acids, the breakdown of amino acids for energy production, and the maintenance of nitrogen balance in the body.

The structure of transaminases consists of a protein chain composed of several domains. These domains are responsible for binding the substrate molecules and facilitating the transfer of the amino group.

The catalytic activity of transaminases relies on the presence of a specific cofactor called pyridoxal 5′-phosphate (PLP), which is derived from vitamin B6. PLP binds to the active site of the enzyme and acts as a coenzyme, participating in the transfer of the amino group between the amino and keto acids.

ALT and AST: Liver-Specific Transaminases

ALT and AST are two transaminases that are predominantly localized in the liver.

ALT, also known as serum glutamate pyruvate transaminase (SGPT), is primarily found within liver cells, with a smaller amount present in the kidneys, heart, and skeletal muscles. AST, also known as serum glutamic-oxaloacetic transaminase (SGOT), is found in the liver, heart, skeletal muscles, and other organs.

Although ALT and AST are present in various tissues, their levels are significantly higher in the liver. This makes them reliable markers for detecting liver damage or disease.

When liver cells are injured or destroyed, ALT and AST leak into the bloodstream, leading to elevated levels of these enzymes in the blood.

Role of Transaminases in Liver Damage

Liver damage can be caused by various factors, including viral infections (such as hepatitis B and C), alcohol abuse, drug-induced liver injury, fatty liver disease, autoimmune diseases, and genetic disorders.

When liver cells are damaged, either by inflammation, injury, or cell death, ALT and AST are released from the hepatocytes into the bloodstream.

Monitoring the levels of transaminases, particularly ALT, can help identify liver damage at an early stage. As the liver regenerates, the damaged cells release higher amounts of ALT and AST.

Therefore, an increase in transaminase levels can indicate ongoing liver damage or disease progression.

Interpreting Transaminase Levels

Transaminase levels are measured through a blood test called a liver function test (LFT). The normal ranges for ALT and AST can vary slightly depending on the laboratory and the measuring techniques used.

In general, ALT levels in healthy adults range from 7 to 55 units per liter (U/L), while AST levels range from 8 to 48 U/L.

Elevated levels of ALT can indicate liver damage, particularly hepatocellular damage. ALT levels higher than the upper limit of the reference range suggest liver injury. The degree of elevation is generally proportional to the extent of liver damage.

However, it is important to note that ALT levels can also be influenced by factors such as muscle injury, certain medications, and conditions affecting red blood cell breakdown.

AST levels, on the other hand, are not specific to liver damage and can also be elevated in conditions affecting other organs, such as the heart or skeletal muscles. Therefore, ALT is considered a more liver-specific marker compared to AST.

Common Causes of Elevated Transaminase Levels

Several factors can cause an increase in transaminase levels. Some of the most common causes include:.

Hepatitis

Hepatitis, particularly viral hepatitis, is a major cause of liver damage and elevated transaminase levels. Hepatitis B and C viruses can infect liver cells, leading to inflammation and injury.

The release of ALT and AST into the bloodstream results in increased transaminase levels. Chronic hepatitis can cause long-term liver damage if left untreated.

Alcohol-Related Liver Disease

Excessive alcohol consumption can lead to liver damage, known as alcohol-related liver disease (ALRD). ALRD encompasses a range of conditions, including fatty liver, alcoholic hepatitis, and cirrhosis.

ALT levels are often elevated in individuals with alcohol-related liver disease.

Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is characterized by the accumulation of fat in the liver. It is commonly associated with obesity, type 2 diabetes, and metabolic syndrome.

NAFLD can cause liver inflammation and damage, leading to elevated ALT levels.

Medications and Toxins

Certain medications and toxins can affect liver function and cause liver damage, leading to increased transaminase levels. Examples include acetaminophen (paracetamol) overdose, statins, anti-seizure medications, and some herbal or dietary supplements.

Autoimmune Hepatitis

Autoimmune hepatitis is a chronic inflammatory liver disease characterized by immune system dysfunction. The body’s immune system mistakenly attacks liver cells, leading to inflammation and liver damage.

Elevated ALT levels are often observed in individuals with autoimmune hepatitis.

Clinical Significance and Monitoring

Transaminases, particularly ALT, are widely used as primary markers of liver health. Monitoring transaminase levels can help diagnose liver disease, determine the extent of liver damage, and monitor the response to treatment.

Additionally, they can assist in identifying potential liver toxicity associated with certain medications or toxins.

Regular monitoring of transaminases is essential for individuals with known liver conditions or those at risk of liver disease, such as individuals with viral hepatitis, alcohol abuse history, or obesity.

Persistent elevation or a significant increase in transaminase levels may indicate disease progression or the need for further investigation.

Conclusion

Transaminases, particularly ALT and AST, are vital markers for assessing liver health and detecting liver damage.

Measuring these enzyme levels through a liver function test can aid in the early diagnosis of liver disease and monitoring treatment response. Elevated transaminase levels should prompt further evaluation to determine the cause of liver damage and develop an appropriate management plan.