ALP

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What is alkaline phosphatase?

Alkaline phosphatase (ALP) is an indicator of liver function tests. It is widely distributed in various organs of the human body. The liver is the most common, followed by the kidneys, bones, intestines, and placenta. When the liver is damaged or obstructed, it enters the blood through the lymphatic tract and hepatic sinusoids. At the same time, due to the bile excretion of the intrahepatic biliary tract, the backflow into the blood causes a significant increase in serum alkaline phosphatase.

Figure 1. Protein structure of ALP.

Introductions

Alkaline phosphatase is not a single enzyme, but a group of isoenzymes. At present, six isozymes of AKP1, AKP2, AKP3, AKP4, AKP5 and AKP6 have been found. The first, second, and sixth species are all from the liver, the third species are derived from bone cells, the fourth species are derived from placenta and cancer cells, and the fifth species are derived from small intestinal villi epithelium and fibroblasts. ALP in serum mainly comes from liver and bones. Most of the serum of growing children comes from osteoblasts and growing osteochondrocytes, and a small amount comes from the liver.

What is an alkaline phosphatase test?

An alkaline phosphatase (ALP) test measures the amount of ALP in your blood. ALP is an enzyme found throughout the body, but it is mostly found in the liver, bones, kidneys, and digestive system. When the liver is damaged, ALP may leak into the bloodstream. High levels of ALP can indicate liver disease or bone disorders.

Reasons for high alkaline phosphatase

Experts pointed out that the causes of high alkaline phosphatase can be divided into physiological causes and pathological causes. Pathological causes are common in hepatobiliary system diseases and bone diseases.

There are 5 specific reasons for the high alkaline phosphatase:

1. Physiological reasons: In children and pregnant women, the alkaline phosphatase in the bone tissue is very active in these cases, so the detection time will be higher.

2. Liver and gallbladder disease: Because the liver cells have the most alkaline phosphatase, if there is a problem with the liver and gallbladder, it will lead to high alkaline phosphatase. When the human body suffers from obstructive jaundice, primary liver cancer, secondary liver cancer, cholestatic hepatitis, etc., liver cells overproduce alkaline phosphatase, which enters the blood through the lymphatic tract and hepatic sinusoids. At the same time, due to bile excretion disorders, the Inflow into the blood, causing high serum alkaline phosphatase.

3. Bone diseases: As alkaline phosphatase is also very active in bone tissue, patients with bone diseases will have high alkaline phosphatase. Such as fracture healing period, rickets, osteoporosis, rickets, bone malignant tumors, etc.

4. Other less common diseases, such as kidney disease, severe anemia, hyperthyroidism, leukemia, etc.

5. Caused by certain drugs. Clinical patients use antibiotics (erythromycin, chloramphenicol, gentamicin, kanamycin, ampicillin, etc.)

Inhibitors

Homoarginine inhibits all mammalian alkaline phosphatase isoenzymes except the placenta (PALP and SEAP), and in a similar way, all other alkaline phosphatase isoenzymes except the intestine and placenta are levamisole Block. Phosphate is another inhibitor that competitively inhibits alkaline phosphatase. Another known example of an alkaline phosphatase inhibitor is [ ( 4-nitrophenyl)methyl] phosphonic acid. In metal-contaminated soil, alkaline phosphatase is inhibited by Cd (cadmium). In addition, temperature enhances the inhibitory effect of Cd on ALP activity, which is manifested as an increase in Km.

References

1. Harada M.; et al. Inorganic pyrophosphatase activity of purified bovine pulp alkaline phosphatase at physiological pH. Journal of Dental Research. 1986, 65 (2): 125–7.
2. Hehir MJ.; et al. Characterization of heterodimeric alkaline phosphatases from Escherichia coli: an investigation of intragenic complementation. Journal of Molecular Biology. 2000, 304 (4): 645–56.