hymecromone and Mucopolysaccharidosis-II

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disorder related to a deficiency in the enzyme iduronate-2-sulfatase (IDS). Clinical trials of enzyme replacement therapy are in progress, but effective treatment will require screening assays to enable early detection and diagnosis of MPS II. Our study evaluated the diagnostic accuracy of IDS protein and enzyme activity measurements in dried blood spots and plasma.. We collected dried-blood-spot and plasma samples from unaffected control individuals and from MPS II patients. We measured IDS protein concentration with a 2-step time-delayed dissociation-enhanced lanthanide fluorescence immunoassay. To measure enzyme activity, we immobilized anti-IDS antibody on microtiter plates to capture the enzyme and measured its activity with the fluorogenic substrate 4-methylumbelliferyl sulfate.. Dried-blood-spot samples from MPS II patients showed an almost total absence of IDS activity (0-0.075 micromol x h(-1) x L(-1)) compared with control blood spots (0.5-4.7 micromol x h(-1) x L(-1)) and control plasma (0.17-8.1 micromol x h(-1) x L(-1)). A dried-blood-spot sample from only 1 of 12 MPS II patients had detectable concentrations of IDS protein (24.8 microg/L), but no IDS protein was detected in plasma from MPS II patients. Ranges for IDS protein in control samples were 25.8-153 microg/L for blood spots and 22.8-349.4 microg/L for plasma.. Measurement of the IDS protein concentration and enzyme activity (as measured by a simple fluorogenic assay with an immune capture technique) enables identification of the majority of MPS II patient samples from both dried blood spots and plasma samples.

Topics: Adolescent; Adult; Animals; Blood Specimen Collection; Calibration; Child; Child, Preschool; CHO Cells; Clinical Enzyme Tests; Cricetinae; Cricetulus; Fluorometry; Humans; Hymecromone; Iduronate Sulfatase; Immunoassay; Indicators and Reagents; Infant; Middle Aged; Mucopolysaccharidosis II; Plasma; Recombinant Proteins

Mucopolysaccharidosis type II (MPS II, Hunter syndrome, OMIM 309900) is an X-linked recessive lysosomal storage disease resulting from a deficiency of iduronte-2-sulphate sulphatase (IDS). The present study aimed to establish an enzyme assay method for IDS activity for carrying out postnatal and prenatal diagnosis of MPS II by means of IDS activity assay on plasma, uncultured chorionic villi (CV) and cultured amniotic fluid cells (AF cell) using a new synthesized substrate.. A fluorigenic substrate (4-methylumbelliferyl-alpha-iduronate-2-sulphate, MU-alpha-Idu-2S) was used for the assay of IDS activity. IDS activity in plasma was determined for diagnosis of the proband. Prenatal diagnosis in 10 pregnancies at risk was carried out according to IDS activity on uncultured CV at 11th week or on cultured AF cell at 18th week of gestation. At the same time, IDS activity was also determined in the maternal plasmas to observe the change of IDS activity in pregnancy. The fetal sex determination was performed by PCR amplification of the ZFX/ZFY genes.. The IDS activity in plasma of normal controls and obligate heterozygotes were 240.2 - 668.2 nmol/(4 hxml) and 88.7 - 547.9 nmol/(4 hxml), respectively, while the enzyme activities in plasmas were in the range of 0.3 - 18.6 nmol/(4 hxml) in affected male. The IDS activities were 37.2 - 54.9 nmol/(4 hxmg protein) and 21.4 - 74.4 nmol/(4 hxmg protein) in CV and cultured AF cells respectively. Out of 50 suspected cases, 46 were diagnosed as having MPS II and 4 were excluded. Prenatal diagnosis was performed on 10 pregnancies at risk. Four of 5 male fetuses [IDS activity were 4.7, 1.8, 7.0 nmol/(4hxmg protein) in CV, 0.6 nmol/(4 hxmg protein) in AF cell] were diagnosed as having MPS II and the other 5 fetuses were normal females [IDS activity were: 48.7, 5.9, 25.2 nmol/(4 hxmg protein) in CV, 55.2, 40.9 nmol/(4 hxmg protein) in AF cell]. Increased IDS activity was observed in plasma of the pregnant women with unaffected fetuses, while the IDS activity decreased in pregnancies with affected fetuses. IDS activity of one female fetus was very low [5.9 nmol/(4 hxmg protein)], but the IDS activity in maternal plasmas increased, this fetus was a normal female.. The method using a synthesized fluorigenic 4-methylumbelliferyl-substrate was a sensitive, rapid and convenient assay of IDS activity and was reliable for early prenatal diagnosis. Determination of fetal sex would be helpful in excluding the female fetus with low IDS activity from being considered as an affected male fetus. It would be further helpful if IDS activity in maternal plasma was taken into account.

Topics: Amniotic Fluid; Cells, Cultured; Child; Child, Preschool; China; Chorionic Villi; Chorionic Villi Sampling; Enzyme Assays; Female; Fetus; Fluorometry; Heterozygote; Humans; Hymecromone; Iduronate Sulfatase; Iduronic Acid; Karyotyping; Male; Mucopolysaccharidosis II; Polymerase Chain Reaction; Pregnancy; Pregnancy, High-Risk; Prenatal Diagnosis; Reference Values; Sex Factors

4-Methylumbelliferyl-alpha-iduronate 2-sulphate was synthesized and shown to be a specific substrate for the lysosomal iduronate-2-sulphate sulphatase (IDS). Fibroblasts (n = 17), leukocytes (n = 3) and plasmas (n = 9) from different MPS II patients showed < 5% of mean normal IDS activity. The enzymatic liberation of the fluorochrome from 4-methylumbelliferyl-alpha-iduronate 2-sulphate requires the sequential action of IDS and alpha-iduronidase. A normal level of alpha-iduronidase activity was insufficient to complete the hydrolysis of the reaction intermediate 4-methylumbelliferyl-alpha-iduronide formed by IDS. A second incubation step in the presence of excess purified alpha-iduronidase is needed to avoid underestimation of the IDS activity.

Topics: Fibroblasts; Fluorometry; Humans; Hydrogen-Ion Concentration; Hymecromone; Iduronate Sulfatase; Iduronic Acid; Leukocytes; Lysosomes; Mucopolysaccharidosis II; Substrate Specificity