Anatomy & Organs

Liver Enzymes – Function & Diseases

Liver Enzymes

Liver enzymes are enzymes that are specific to liver cells (hepatocytes). In clinical parlance, they are often also referred to as liver values . An increase in certain enzymes is an indication of liver damage, while other enzymes are found at lower levels in liver disease.

What are liver enzymes?

In liver disease, liver enzymes often provide important clues as to what type of disease it is. In general, the body needs enzymes to maintain the performance of the metabolism . If the liver cells are damaged, the liver enzymes in the blood serum are increased.

Depending on the elevated enzyme, conclusions can then be drawn about the type of disease. Cell damage can be caused by alcohol , viral infections, tumors or poisoning. Liver enzymes that are commonly measured include:

  • Gamma-Glutamyltransferase (Gamma-GT)
  • Glutamate dehydrogenase (GLDH)
  • Aspartate aminotransferase (AST, ASAT)
  • Alanine aminotransferase (ALT, ALAT)
  • alkaline phosphatase

Function, effect & tasks

The liver, which is located in the right upper abdomen, is involved in many of the body’s breakdown and build-up processes. Important proteins are produced here, and hormones are broken down in the liver and the red blood pigment is broken down. 

The bile substances are then produced from the red blood pigment, which together with other substances form the bile fluid. This is excreted in the small intestine and plays an important role in fat digestion. In addition, the liver also stores glycogen , copper , and iron , respectively , and breaks down food components that can then be used by the body. All of these processes require enzymes that mediate chemical reactions. However, they are not consumed in the process. For this reason they are also called catalysts.

Such enzymes include, for example, transaminases such as glutamate pyronate transaminase or glutamate oxalacetal transaminase. They occur in the liver in very large quantities and are released when liver cells are damaged. The aspartate aminotransferase is important for the respiratory chain or the malate-aspartate shuttle and ensures that the L-amino group is transferred to an a-keta acid. ALT plays an important role in the glucose-alanine cycle, catalyzing the reaction L-alanine + a-ketoglutarate = pyruvate + L-glutamate. Gamma-glutamyl transferase transfers the glutamyl residue of glutathione (GSH) to peptides or water, thereby breaking down glutathione.

Cysteine ​​occurs in glutathione   , which is then transported into the cells. Here glutathione is then built up again. The role of alkaline phosphatases, which act as markers for various  skeletal and liver diseases, has not yet been fully clarified. If there is liver disease, the enzymes are determined, giving the doctor information about the extent and type of disease. The extent of the increase in the respective enzyme indicates the extent of the damage.

Formation, Occurrence, Properties & Optimal Values

The production of liver enzymes takes place in the liver cells. The various enzymes contribute to accelerating the metabolic processes that take place in the liver cells. If the liver cells are damaged, the enzymes are released and get into the blood .

One of the most important liver enzymes is glutamic-oxaloacetic transaminase, which is found in the liver, skeletal muscles and heart muscle and is now also known as aspartate aminotransferase (AST). In the cytoplasm of liver cells, the enzyme glutamic pyruvic transaminase or alanine aminotransferase (ALT) can be found. Pyruvate is formed from alanine aminotransferase and alanine from excess nitrogen.

A so-called membrane-bound enzyme is gamma-glutamyl transferase (y-GT), which is found in the liver, kidneys , small intestine , spleen and pancreas . Alkaline phosphatases are enzymes that can break down phosphoric acid monoesters and can be found in the liver, bones , kidneys or small intestine.

Diseases & Disorders

Liver enzymes are determined in the diagnosis of liver diseases. To do this, the doctor takes blood from the patient, which is then examined in the laboratory. Important syndromes that can lead to liver damage are autoimmune-inflammatory diseases, hepatocellular insufficiency, cholestasis and cytolysis. 

The cause can be neoplastic, autoimmune, traumatic, toxic or infectious. In cytolysis syndrome, liver cells are dissolved and the cell contents get into the blood. The enzyme that predominates in cytolysis is the ALAT. ASAT predominates in cirrhotic-stage disease or in alcohol-induced  hepatitis  . If the ASAT is moderately increased, this can indicate muscle cell damage, which can be confirmed by a subsequent determination of the so-called creatine kinase. The cholestasis syndrome indicates a disturbance in bile excretion or synthesis. A distinction can be made between obstructive and non-obstructive cholestasis.

In obstructive cholestasis, for example, the bile ducts are obstructed by gallstones, while in non-obstructive cholestasis the epithelial cells in the bile ducts are damaged, resulting in reduced bile acid excretion. In cholestasis, there is an increase in the enzymes GT and ALP. If the value of the ALP is normal and only the enzyme GT is elevated, chronic  alcoholism is usually  present. If only the AlP value is increased, this indicates a bone disease.

In the case of hepatocellular insufficiency, the liver function is damaged, as a result of which albumin synthesis is reduced and protein metabolism or the conversion of fats and sugars is slowed down. In the autoimmune-inflammatory syndrome, the immunoglobulins rise , an increased IgA indicates alcohol-induced cirrhosis.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.