Fucosidase

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α-L-Fucosidase (AFU) is a lysosomal acid hydrolase. In 1980, French scholar Deugnier et al. found that AFU has good sensitivity in diagnosing hepatocellular carcinoma, with a high positive rate, which is the highest rate of AFP positive More than three times, it is of great value in the diagnosis of AFP-negative cases and small cell liver cancer, and is a useful indicator for early diagnosis of primary liver cancer. And it has been confirmed by many researches. The α-L-fucosidase in tissues is an enzyme encoded by the FUCA1 gene in humans. α-Fucosidase is an enzyme that breaks down fucose. Fucose poisoning is an autosomal recessive lysosomal storage disease caused by defective α-L-fucosidase and fucose accumulation. In the organization. The different phenotypes include clinical features such as deterioration of the nervous system, growth retardation, visceral hypertrophy and severe early onset. Thicker facial features, longer survival forms, physical vasodilatation, spasms, and delayed psychomotor development; and another unusual form of vertebral osteophytes, pulmonary tracheal dysplasia.

Figure 1. Protein structure of Alpha-L-fucosidase.

Chemical characteristics

AFU is mainly involved in the catabolism of various fucosyl-containing glycolipids, glycoproteins, mucopolysaccharides and other macromolecular substances. It is widely present in lysosomes and body fluids of various tissues of the human body. Serum, urine, saliva, tears and other specimens are acceptable. The specimens should be clarified and stored at 4°C for 3 days, and at -20°C for 3 months. Avoid repeated freezing and thawing. Hemolysis, jaundice, hyperlipidemia, and contaminated specimens seriously affect the results.

Detection method

• Fluorescence method

Use AFU to hydrolyze 4-methylumbelliferone α-L-fucopyranoside to release 4-methylumbelliferone, stop the reaction with alkaline buffer, and make the product show fluorescence, using 360nm or 365nm Excitation wavelength and emission wavelength of 400nm or 448nm were used to detect the fluorescence intensity, and the enzyme activity was calculated according to standard curves prepared with different concentrations of 4-methylumbelliferone. This method is highly sensitive, and the minimum detection limit is 0.06U/L.

• Colorimetric method

4-nitrobenzene α-L-fucopyranoside is used as a substrate to release 4-nitrophenol by AFU hydrolysis. The reaction is also terminated with alkaline buffer to make 4-NP appear significantly yellow. Read the absorbance A at the specified wavelength. Using pure 4-NP as a standard, the AFU activity was calculated using the standard curve or 4-NP molar absorbance. This method is simple and has low equipment requirements and is widely used at home and abroad.

Clinical significance

Liver cancer

The AFU activity in the serum of patients with primary liver cancer is not only significantly higher than that of normal controls, but also significantly higher than that of metastatic liver cancer, cholangiocytic cells, malignant mesothelioma, malignant hemangioendothelioma, liver cirrhosis, congenital liver cysts and other benign livers Space-occupying lesions. The positive rate for the diagnosis of primary liver cancer is 64%-84%, and the specificity is about 90%.

Figure 2. Liver cancer

Pregnancy and ovarian cancer

Studies have shown that plasma AFU increases as the number of weeks of gestation increases, and after natural delivery or artificial termination of pregnancy, it drops rapidly and returns to normal within 5 days. The activity of serum AFU in patients with ovarian cancer decreases, and it has nothing to do with disease stage, tumor burden, histological type and tumor differentiation. Decreased serum AFU activity in patients with benign and malignant ovarian cancer may be related to genetic factors

Figure 3. Ovarian cancer.

Other

In patients with fucosidase storage, due to lack of AFU or reduced activity in tissues, organs and body fluids, disorders of glycoprotein or glycolipid metabolism are caused. Serum AFU is elevated in patients with gastric cancer, but does not increase in acute pancreatitis, but decreases when cystic fibrosis is accompanied by pancreatitis, and serum AFU activity decreases in progressive pyramidal dystrophy.

81.2% of patients with primary liver cancer have increased serum AFU levels. Combined detection with AFP can increase the positive rate of primary liver cancer diagnosis by 93.1%.

Dynamic observation is of great significance for judging the curative effect, prognosis and recurrence of liver cancer.

Serum AFP can also increase in metastatic liver cancer, lung cancer, breast cancer, ovarian cancer, and uterine cancer; it can also increase slightly in liver cirrhosis, chronic hepatitis, gastrointestinal bleeding, etc.