A coupled enzyme assay for measurement of sialidase activity

Optimization of an Inclusion Body-Based Production of the Influenza Virus Neuraminidase in Escherichia coli

Neuraminidase (NA), as an important protein of influenza virus, represents a promising target for the development of new antiviral agents for the treatment and prevention of influenza A and B. Bacterial host strain Escherichia coli BL21 (DE3)pLysS containing the NA gene of the H1N1 influenza virus produced this overexpressed enzyme in the insoluble fraction of cells in the form of inclusion bodies. The aim of this work was to investigate the effect of independent variables (propagation time, isopropyl β-d-1-thiogalactopyranoside (IPTG) concentration and expression time) on NA accumulation in inclusion bodies and to optimize these conditions by response surface methodology (RSM). The maximum yield of NA (112.97 ± 2.82 U/g) was achieved under optimal conditions, namely, a propagation time of 7.72 h, IPTG concentration of 1.82 mM and gene expression time of 7.35 h. This study demonstrated that bacterially expressed NA was enzymatically active.

Sialidase substrates for Sialdiase assays - activity, specificity, quantification and inhibition

Sialidases are glycosidases responsible for the removal of sialic acid (Sia) residues (desialylation) from glycan portions of either glycoproteins or glycolipids. By desialylation, sialidases are able to modulate the functionality and stability of the Sia-containing molecules and are involved in both physiological and pathological pathways. Therefore, evaluation of sialidase activity and specificity is important for understanding the biological significance of desialylation by sialidases and its function and the related molecular mechanisms of the physiological and pathological pathways. In addition, it is essential for developing novel mechanisms and approaches for disease treatment and diagnosis and pathogen detection as well. This review summarizes the most recent sialidase substrates for evaluating sialidase activity and specificity and screening sialidase inhibitors, including (i) general sialidase substrates, (ii) specific sialidase substrates, (iii) native sialidase substrates and (iv) cellular sialidase substrates. This review also provides a brief introduction of recent instrumental methods for quantifying the sialidase activity, such as UV, fluorescence, HPLC and LC-MS methods.

The Relationship of Various Factors in the Pathogenesis of Atherosclerosis

In this study we investigated the levels of lipid parameters, fibronectin, tissue-type plasminogen activator and plasminogen activator inhibitor (t-PA-PAI-1) complex and si alidase in patients with coronary heart disease and a control group. Total cholesterol, triglyceride, low-density lipoprotein (LDL), and very-low-density lipoprotein (VLDL) cholesterol and lipoprotein Lp(a), levels in patients with coronary heart disease were found to be significantly higher than in the control group (p < .001). High-density lipoprotein (HDL) cholesterol levels in patient group were significantly lower than control group (p < .001). Plasma fibronectin and t-PA-PAI-1 complex levels in patients with coronary heart disease were found to be significantly higher than control group (p < .05 and p < .001, respectively). In addition, we found that serum sialidase levels in patients with coronary heart disease were significantly higher than in the control group (p < .001). The electrophoretic mobility of lipoproteins from patients with coronary heart dis ease was found to be greater than those from the control group. As a result Lp(a) may play an important role in the pathogen esis of atherosclerosis by causing foam cell formation because of interacting with LDL or fibronectin and by interfering with the fibrinolytic system because of binding to plasminogen re ceptors. In addition, modifications of Lp(a) (including desi alylation) may effect these events. Key words: Coronary heart disease—tPA-PAI-1 complex-Fibronectin-sialidase-Lipid parameters.

The Relationship Between Lipid Peroxidation and LDL Desialylation in Experimental Atherosclerosis

ABSTRACT High serum total cholesterol concentration has been strongly connected with atherosclerosis in numerous studies. Being the main carrier of cholesterol in blood, low-density lipoprotein (LDL) is also the principal lipoprotein causing atherosclerosis. Sialic acids are a family of amino sugars that are commonly found as terminal oligosaccharide residues on glycoproteins and are sialylated on their apolipoprotein and glycolipid constituents. In several studies, it was demonstrated that LDL has a 2.5- to 5-fold lower content of sialic acid in patients with coronary artery disease compared with healthy subjects. The role of oxidatively modified LDL in the pathogenesis has been well documented. These studies have focused on modifications in the lipid and protein parts of LDL. But recently, desialylated LDL and its relation with the oxidation mechanisms have received attention in the pathogenesis of atherosclerosis and coronary artery disease (CAD). From these points, we have performed atheroma plaques in an experimental atherosclerosis model with rabbits and examined the LDL and plasma sialic acid and thiobarbituric acid reactive substance (TBARS) levels in the same model. We also have determined serum sialidase enzyme activities relevant with these parameters. LDL sialic acid levels were significantly decreased in the progression of the atherosclerosis (by the 30th, 60th, and 90th days). LDL and plasma TBARS levels and plasma sialidase enzyme activities were significantly elevated by the same time periods. In conclusion, serum sialidase enzyme may play an important role in the desialylation mechanism, and reactive oxygen substance (ROS) may affect this reaction.

Cell surface sialic acid inhibits Cx43 gap junction functions in constructed Hela cancer cells involving in sialylated N-cadherin

Numerous studies have shown that changes in the glycan structures of cells correlate with tumorigenesis, however, a casual link between the altered glycan structures and the abnormal GJIC in cancer cells is rarely studied. In this paper, we investigated the effects of sialic acid on the Cx43 gap junction functions, and clarified its potential mechanisms thereby. Sialidase significantly increased Cx43 gap junction functions in constructed Cx43-Hela cells along with down-regulation of cell surface sialic acid, which is dramatically reversed by sialidase inhibitor NeuAc2en. Further study indicated that sialidase failed to affect Cx43 at either protein or phosphorylation level, instead, it induced a considerable fraction of Triton X-100 insoluble, as compared with the untreated cells. We also found that sialidase treatment reduced the N-cadherin glycosylation and enhanced both Cx43-ZO-1 interaction and N-cadherin-ZO-1 association. Moreover, sialidase promoted the cell-cell adhesion with elevating N-cadherin binding to β-catenin, accompanied by increasing colocalization of Cx43 with microtubules at the cell periphery. Based on live cell microscopy, with the FARP technology in the Cx43-EGFP-Hela cells, we found that Cx43 in the plague recovered more quickly in sialidase treatment group, indicating that sialidase could promote the Cx43 traffic to the plague. Overall, these studies indicate cell surface sialic acid on cancer cells may suppress Cx43 gap junction functions via inhibiting Cx43 traffic to the plague involving in sialylated N-cadherin, a process that likely underlies the intimate association between abnormal GJIC and glycosylation on cancer development.

Curcumin's effects on sialic acid level and sialidase activity in Ehrlich ascites tumor bearing mice

In this study, we determined curcumin's anticancer and chemopreventive effects in mice bearing Ehrlich ascites tumor by evaluation of cancer biomarkers, sialic acid level and sialidase activity. Both plasma sialic acid level and sialidase activity increased significantly in the mice group with Ehrlich ascites tumor. When the tumor groups fed with curcumin and fed with sesame oil were compared, sialic acid level and sialidase activity in ascites fluid significantly reduced in the group fed with curcumin in addition to the increases of plasma sialic acid level and sialidase activity. The tumor group fed with curcumin lived twice longer than the one fed with sesame oil. Curcumin as a phenolic compound decreased all these parameters in Ehrlich ascites tumors and lengthened survival by 88% in the mice with tumor. We concluded that curcumin has anticancer activity.

Carbohydrate-deficient transferrin and sialidase levels in coronary heart disease

Transferrin is a N-glycosylated glycoprotein and plays an important role in iron transport from sites of absorption and storage to sites of utilization. The main component of normal serum transferrin contains two biantennary glycans, each consisting of 2 mol of sialic acid (Tetrasialo transferrin). Normal serum also contains small amounts of tri- and disialotransferrin. We have undertaken this study to investigate the levels of serum carbohydrate-deficient transferrin (Desialotransferrin) and sialidase levels in patients with coronary heart disease. In patient group, serum desialotransferrin and sialidase levels were found to be significantly higher than control group (p < 0.01 and p < 0.001, respectively). We conclude that increased activity of sialidase may be responsible for increased desialotransferrin in patients with coronary heart disease. Serum desialotransferrin levels may be useful critaria to diagnosis and pathogenesis of coronary heart disease.

Tissue and serum sialidase levels in breast cancer

Breast cancer is both one of the most common and one of the most treatable of all human malignancies. It has been suggested by various investigators that sialic acid increases in the sera of cancerous patients. In cancer patients, an increase in the levels of serum sialic acid may also be due to an increase in the activity of serum or tissue sialidase. The purpose of the present investigation was to determine whether the concentration of sialidase in serum and breast tissue could be used as a tumor marker in breast cancer. In this study; serum sialidase levels in 26 patient with breast cancer and 31 controls were found to be 77.04+/-25.07 U/l and 55.56+/-7.50 U/l, respectively. The mean tissue sialidase levels in 26 breast cancer patients and 13 controls were 39.76+/-17.03 U/g protein and 14.30+/-7.09 U/g protein, respectively. Serum and tissue sialidase levels in breast cancer were significantly higher than those found in the control group (P < 0.001). The mean serum and tissue sialidase levels in 14 Grade I-II and 12 Grade III breast cancer patients were found to be 67.73+/-11.87 U/l and 33.41+/-12.17 U/g protein and 87.89+/-31.94 U/l and 47.17+/-19.30 U/g protein, respectively. Also we found a significant difference between the levels of serum and tissue sialidase in Grade I-II and III (P < 0.05).