The liver is a vital organ of the digestive system present in vertebrates and some other animals. It has a wide range of function including detoxification, protein synthesis and production of biochemical necessary for digestion. The liver is necessary for survival. There is currently no way to compensate for the absence of the liver in the long term although new liver dialysis techniques can be used in the short term. The organ plays a major role in metabolism and has a number of functions in the body including glycogen storage, decomposition of red blood cells, plasma protein synthesis, hormone production and detoxification.
The liver lies below the diaphragm in the abdominal pelvic region of the abdomen. It produces bile, an alkaline compound which aids in digestion via the emulsification of lipids. The liver’s highly specialized tissues regulate a wide variety of high-volume biochemical reactions, including the synthesis and breakdown of small and normal vital functions (Maton et al., 1993).
Liver enzymes
Enzymes are proteins found in the body that speed up (catalyze) certain chemical reactions. Liver enzymes perform these jobs within the liver. Liver enzymes test formerly called live r function tests that detect inflammation and damage of the liver. They also check how well the liver is working; they give information about the state of a patient’s liver (Lee, 2009). Liver enzymes includes
- Alanine amino transaminase (ALT)
- Aspartate amino transaminase (AST)
- Alkaline phosphate (ALP)
- Gamma-glutamyl transferase (GGT)
- 5’nucleotidase
ALT and AST are collectively known as transferase or transaminase. They are the two common liver enzymes. ALP, GGT and 5’nucleotidase are collectively known as cholestatic liver enzymes, their function is the production of bile which helps digest fat. Elevation of these enzymes can indicate the presence of liver disease.
Alanine amino transaminase (ALT)
It is also called Alanine amino transaminase or serum glutamic pyruvate transaminase (SGPT). It is found in the plasma and in various body tissues but is most commonly associated with the liver. It reference range is 10 – 40 iu/L (Wang et al., 2012).
It catalyzed the transfer of an amino group from L-alanine to -ketoglutarate, the product of this reversible transferase reaction being pyruvate and L-glutamate. ALT (and all transaminase) requires the co-enzymes pyridoxamine in the first phase of the reaction, when an Amino acid is converted into a keto acid.
Clinical significance of alanine amino transaminase (ALT)
It is commonly measured clinically as a part of a diagnostic evaluation of the patocelluler injury to determine liver health. When used in diagnostics, it is almost always measured in international units/liter (IU/L) (Wang et al., 2012). Wang et al., 2012 also reported that while source vary on specific reference range values for patients, 10 – 40 IU/L is the standard reference range for experimental studies. Significantly, elevated level of ALT often suggest the existence of liver damage as it is predominant in the liver, hence it is commonly used as a way of screening for liver problems.
Aspartate aminotransaminase (AST)
Aspartate aminotransaminase (AST) or aspartate aminotranferase also known as serum glutamic oxaloacetic transaminase (SGOT) catalyzes the reversible transfer of an -amino group between aspartate and glutamate and such is an important enzymes in amino acid metabolism. AST is found in the liver, heart, skeletal muscle, kidney, brain and red blood cells.AST catalyzes the interconversion of aspartate and -ketoglutarate to oxaloacetate and glutamate.
Aspartate + -ketoglutarate ßà oxaloacetate + glutamate.
Clinical significance of aspartate aminotransaminase (AST)
It is commonly measured clinically as a part of a diagnostic evaluation of hepatocelluler injury to determine liver health. AST and ALT are considered to be two of the most important tests to detect liver injury, although ALT is more specific for the liver than AST (Nyblom, et al., 2006).
References
Lee MB. (2009). ”Basic skills in interpreting Laboratory data. ASHP. Pp.259.
Maton A., Jean Hopkins, Charles Williams Mclaughlin, Susan Johnson, Maryanna Qoun Warner, David lahart and J.UD. Wright. (1993). “ human biology and health”. Englewood cliffs, New Jersey, U.S.A. Prentice hall. 50(12): 847-852. I
Nyblom, H., E. Bjornsson, M. Simren, F. Aldenborg, S. Almer and Olsson, (2006). The AST/ALT ratio as an indicator of cirrhosis in patients with PBC, Liver Int., 26(7): 840-845.
Wang C.S., Chang Ting-Tsung, Yao wei-Jen, Wang shan Tair and Chou pesus. (2012). ”impact of increasing alanine aminotansferase levels within normal range on incident diabetes”. Formed med assoc 111(4): 201-208.
