Secretion of beta-N-acetylglucosaminidase isoenzymes by normal human fibroblasts

We still have a long way to go to effectively deliver genes!

Gene therapy is emerging as a revolutionary alternative to conventional therapeutic approaches. However, its clinical application is still hampered by the lack of safe and effective gene delivery techniques. Among the plethora of diverse approaches used to ferry nucleic acids into target cells, non-viral vectors represent promising and safer alternatives to viruses and physical techniques. Both cationic lipids and polymers spontaneously wrap and shrink the genetic material in complexes named lipoplexes and polyplexes, respectively, thereby protecting it and shielding its negative charges. The development of non-viral vectors commenced more than two decades ago. Since then, some major classes of interesting molecules have been identified and modified to optimize their properties. However, the way towards the final goal of gene delivery, i.e. protein expression or gene silencing, is filled with obstacles and current non-viral carriers still have concerns about their overall efficiency. We strongly believe that the future of non-viral gene delivery relies on the development of multifunctional vectors specifically tailored with diverse functionalities that act more like viruses. Although these vectors are still a long way from clinical practice they are the ideal platform to effectively shuttle the genetic material to target cells in a safe and controlled way. In this review, after briefly introducing the basis of gene delivery and therapeutic applications we discuss the main polymeric and lipidic vectors utilized for gene delivery, focusing on the strategies adopted to overcome the major weaknesses inherent to their still limited activity, on the way towards ideal multifunctional vectors.

The mechanism of cell death in human cultured colon adenocarcinoma cell line COLO 201 induced by beta-D-N-acetylglucosaminyl-p-nitrophenol

COLO 201, human colon adenocarcinoma cells were incubated with artificial primers, p-nitrophenyl-glycoside derivatives at 1.0 mmol (mM) in the medium containing 10% fetal bovine serum to detect sugar chain elongation. However, when p-nitrophenyl-beta-N-acetylglucosamine (beta-GlcNAc-PNP) was added, the medium changed color to yellow and the cells were dead. To explain this finding, the cells were incubated with 1.0 mM each of beta-GlcNAc-PNP and 4-methylumbelliferyl-beta-N-acetylglucosamine, then the number of living cells was measured in a time course. In beta-GlcNAc-PNP, the living cells were decreased at 24 hours. The cells were survived with N-acetylglucosamine, whereas in the presence of p-nitrophenol (PNP) the living cells were decreased. It was suggested that PNP released from beta-GlcNAc-PNP induced the cell death. Activity of beta-D-N-acetylglucosaminidase was detected in fetal bovine serum. It was shown that PNP induced the cell death in time-and-dose dependent manner. Genomic DNA from COLO 201 analyzed by agarose gel electrophoresis was fragmentated. PNP analogues were tested for toxicity, and the results suggested that the phenolic OH-group linked to benzene ring and nitro-group linked to the structure in para-form (PNP) was the most effective.

Elevated levels of N-acetyl-beta-glucosaminidase in affective disorders and chemical dependence

Levels of N-acetyl-beta-glucosaminidase (NAG) were examined in 575 patients with various psychiatric diagnoses and 38 non-ill controls. Ten percent of affectively disordered patients and 19% of chemically dependent patients had abnormal NAG levels, whereas none of the 38 controls did (P less than 0.05 and P less than 0.003 respectively). Other psychiatric diagnostic groups were not associated with abnormal levels of this enzyme.

Phorbol ester-induced protein kinase C translocation and lysosomal enzyme release in normal and cystic fibrosis fibroblasts

The ability of the tumor-promoting phorbol ester 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) to induce protein kinase C (PKC) translocation and lysosomal enzyme release was examined in skin fibroblasts from normal subjects and from patients with cystic fibrosis (CF). As compared to normal fibroblasts, those CF exhibited: (i) an increased sensitivity to the effect of PMA on the disappearance of PKC from cytosolic fractions as well as a greater and earlier recovery, in the membrane fraction, of the PKC activity lost in the cytosolic fraction; (ii) an earlier response to PMA for its effect on beta-N-acetylglucosaminidase release. In contrast, the inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate (4 alpha PDD) proved ineffective in inducing PKC translocation and beta-N-acetylglucosaminidase release in both normal and CF fibroblasts. The data suggest a defect in the regulation of PKC activity in CF fibroblasts, which may lead to altered secretion.

The in vitro effect of gold complexes on bone resorption

Mouse calvaria were maintained in organ culture without serum additives. The effects of three gold complexes--aurothioglucose, aurothiomalate, and auranofin--on active bone resorption (45Ca release) and hydroxyproline synthesis were determined. The influence of these compounds on DNA and protein synthesis and lysosomal enzyme release from calvaria was also assessed. All gold complexes reduced bone resorption to some extent, with auranofin being the most potent within a narrow concentration range (10(-6) M). This concentration of auranofin also significantly inhibited collagen synthesis, although DNA and protein synthesis were unaffected. None of the compounds tested appeared to mediate their action via significant inhibition of lysosomal enzyme release.

Glycosidases in cancer and invasion

Glycosidases have been demonstrated to be elevated in the interstitial fluid of tumors, sera of animals and patients with tumors, and in some tumor tissue as compared to normal adjacent tissue. Elevations of serum beta-N-acetylglucosaminidase and beta-glucuronidase most commonly have been found to occur and these enzymes have been shown to be secreted into the extracellular medium by many different tumor cell types in vitro. The mechanism of cellular release of these hydrolytic enzymes probably involves tumor lysosomal exocytosis. Increased tumor glycosidase levels may promote increased tumor cell shedding from primary tumors, local invasion and perhaps be responsible directly, or indirectly for structural changes in tumor cell surface glycoconjugates. These cell surface changes could facilitate tumor cell thrombus formation, secondary site implantation and attachment in the microcirculation to endothelial cells and/or subendothelial basement membrane components. Other studies have demonstrated a correlation between metastatic cell potential and increased endoglycosidase and polysaccharide lyase activity. Generally, metastatic tumor cell variants have been found to be more invasive and capable of degrading proteoglycan basement membrane components, in part due to these increased levels of degradative enzymes. Hence, it is of considerable interest to develop inhibitors against these enzymes. Initial studies with glucuronidase inhibitors in the therapy of bladder tumors have been promising and with the advent of better agents and the use of appropriate in vitro metastatic models it may be possible to design and develop agents which interfere in various metastatic events and limit tumor progression.

Inhibition of prostaglandin action and bone resorption by copper

Mouse calvaria were maintained in organ culture without serum additives. The effects of Cu2+ on bone resorption and on the synthesis and action of prostaglandins were studied. Non-toxic concentrations of copper sulphate (5 microM) were found to decrease active resorption, measured by 45Ca release, to 54% control values (p less than 0.001), while prostaglandin F (PGF), prostaglandin E2 (PGE2), and 6-keto-prostaglandin F1 alpha, (6-keto-PGF1 alpha), determined by radioimmunoassay, were increased above controls (p less than 0.05). These effects of Cu2+ on prostaglandin synthesis were confirmed by the isolation and quantitation of [3H]-labelled metabolites released from calvaria which had been pre-labelled with [3H]-arachidonic acid. PGE2, PGF2 alpha, 6-keto-PGF1 alpha, and thromboxane B2 (TxB2) were all higher in copper-exposed calvaria, but their relative amounts remained unchanged. There was no evidence that Cu2+ influenced the mobilisation of [3H]-arachidonic acid from prelabelled calvaria. The stimulation of bone resorption by exogenous prostaglandins was decreased in the presence of Cu2+ (p less than 0.005), while parathormone-mediated bone resorption was virtually unaffected. Cu2+ also increased the inhibition of bone resorption seen with indomethacin (p less than 0.05). In addition to the effects of the metal on prostaglandin action Cu2+ also decreased beta-glucuronidase activity in the media to 86% of the control values (p less than 0.001). The action of Cu2+ in inhibiting bone resorption in vitro appears complex but does not involve inhibition of prostaglandin synthesis. It is likely that Cu2+ has more than one inhibitory locus.

Direct enzyme transfer from lymphocytes is specific

Lymphocytes are known to interact directly with other cells in vivo and in vitro, and have recently been shown to transfer the lysosomal enzyme, beta-glucuronidase, to fibroblasts from patients with an inherited deficiency of the enzyme. This process requires cell-cell contact, is unaffected by inhibitors of 'classical' receptor-mediated endocytosis and is abolished by inhibitors of protein synthesis. Although it is not yet known to what extent the transfer of enzymes by direct cellular interaction is a general phenomenon, a similar mechanism could possibly be involved in the transfer of other lysosomal enzymes in vivo and in the exchange of protein in vitro. We show here that the direct transfer of enzymes from lymphocytes to fibroblasts is restricted to only certain lysosomal enzymes.

Serum levels of glycosyltransferases and related glycoproteins as indicators of cancer: biological and clinical implications

Many studies have suggested that malignant transformation is associated with fundamental changes in the cell surface; similar changes have been described for normal stem cells and cells of embryonic or fetal origin. There is now evidence that the tumor cell secretes or sheds glycoproteins and glycosyltransferases into the surrounding medium and into serum. There are claims that some of these serum glycoproteins and glycosyltransferases are associated with, or specifically related to, the extent of tumor growth and may serve as a cancer marker. A cancer-associated galactosyltransferase isoenzyme (GT-II) has been described and purified. Different isoelectric forms of fucosyltransferase have also been described as indicative of malignancy. The articles to be published in CRC Critical Reviews in Clinical Laboratory Sciences will analyze the evidence for the association of these membrane factors with tumor growth. In order to better understand the possible significance of altered glycoproteins and of increased or different forms of glycosyltransferases during tumor growth, recent data on glycoprotein synthesis will be discussed including the new concepts on the control of glycoprotein synthesis through lipid intermediates. The possible mechanisms whereby malignant transformation could alter glycoprotein synthesis will be discussed with particular emphasis on the significance of these alterations to the biology of the malignant cell. Changes in surface membrane glycoproteins have long been implicated in the ability of a cell to metastasize. Secretion and/or shedding of the cell surface may also be important in the process of metastasis and in altering the host immune response. Detection and the study of these "shed" materials in patients appear to be indicating a new approach to cancer biology detection and therapy.

Molecular forms of beta-hexosaminidase and alpha-mannosidase in cell cultures from patients with mucolipidosis types II and III

Molecular forms of beta-hexosaminidase and alpha-mannosidase were studied using isoelectric focusing in fibroblasts and culture medium from patients with mucolipidosis Types II and III. Compared to controls, no significant aberrations could be found in the isofocusing isoenzyme pattern. Mannose-6-phosphate, which inhibits the uptake of lysosomal enzymes into the cells, was added to the cell cultures from controls without any significant effect on the isofocusing isoenzyme pattern.

Secretion of beta-N-acetylglucosaminidase isoenzymes by cultured cystic fibrosis fibroblasts

Secretion of the lysosomal enzyme beta-N-acetylglucosaminidase (EC 3.2.1.30) by normal and cystic fibrosis fibroblasts has been compared. In contrast to an earlier report, no differences were found in either the rate of secretion, or in the molecular forms of the enzyme secreted by normal fibroblast cultures and cultures initiated from patients with cystic fibrosis. The B isoenzyme of beta-N-acetylglucosaminidase from cystic fibrosis fibroblasts was converted to a more negatively charged form during preincubation for 3 h at pH 5.0 and 37 degrees C. The enzyme from normal fibroblasts was unaffected by this treatment.