Χ-Glutamyl transpeptidase

Gamma-glutamyltransferase (GGT or γ-glutamyl transpeptidase) is an enzyme that plays a crucial role in the metabolism of glutathione, the body's main antioxidant. GGT is involved in the transfer of amino acids across the cellular membrane and in the detoxification of foreign substances. This enzyme is found in many tissues, most notably the liver, kidneys, and pancreas. Elevated levels of GGT in the blood are often used as a biomarker for liver health, indicating liver damage or disease.

Function

GGT catalyzes the transfer of the gamma-glutamyl functional group from molecules such as glutathione to an acceptor that may be an amino acid, a peptide, or water. This process is essential for the breakdown and subsequent resynthesis of glutathione, a critical antioxidant that protects cells from toxins and oxidative stress. By facilitating the recycling of glutathione, GGT plays a vital role in the body's defense mechanism against environmental and metabolic toxins.

Clinical Significance

Elevated levels of GGT are commonly associated with liver diseases, such as hepatitis, cirrhosis, and liver cancer. It can also indicate bile duct obstruction and other diseases related to the biliary system. Because of its sensitivity to alcohol intake, GGT is also used as a marker for excessive alcohol consumption. In clinical settings, GGT tests are often part of liver function tests to assess the state of the liver and biliary system.

Diagnostic Use

The measurement of GGT levels in the blood is a routine part of liver function tests. High levels of GGT may indicate liver damage but cannot specify the cause. Therefore, GGT measurements are usually considered alongside other tests, such as those for alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and bilirubin, to diagnose liver disease or bile duct injury.

Factors Affecting GGT Levels

Several factors can influence GGT levels, including drugs, alcohol consumption, and certain medical conditions. Medications that can increase GGT levels include phenytoin, carbamazepine, and some antibiotics. Obesity, diabetes, and hyperlipidemia are also associated with elevated GGT levels, reflecting the enzyme's role in metabolic syndrome.

Treatment and Management

Addressing high GGT levels involves treating the underlying condition causing the enzyme elevation. This may include lifestyle changes, such as reducing alcohol intake, losing weight, and managing diabetes. In cases of liver disease, specific treatments will depend on the diagnosis, ranging from medication to manage symptoms to more severe interventions like surgery or liver transplantation for advanced diseases.