Glycopeptide storage in fibroblasts from patients with inborn errors of glycoprotein and glycosphingolipid catabolism

Metabolic correction of fucosidosis lymphoid cells by galaptin-alpha-L-fucosidase conjugates

To determine if isolated galaptin, an endogenous galactoside-binding lectin, could serve as a transport vehicle of therapeutic agents to cells, galaptin and alpha-L-fucosidase were coupled using glutaraldehyde. The conjugates were incubated with alpha-L-fucosidase-deficient, EBV-immortalized lymphoid cells from a fucosidosis patient. Conjugates were effectively bound and internalized by the cells in a lactose inhibitable manner. Internalization of conjugate resulted in the reduced accumulation of alpha-L-fucosyl-N-acetylglucosaminylasparagine, a glycopeptide that accumulates in cells of fucosidosis patients, to levels found in lymphoid cells from a healthy individual. Thus, galaptin-alpha-L-fucosidase conjugates may be useful for enzyme replacement therapy of fucosidosis. The concept of using galaptin as a transport vehicle may be applied to the delivery of other compounds to cells bearing galaptin receptors.

Metabolic correction of fucosidosis fibroblasts by human alpha-L-fucosidase

Human alpha-L-fucosidase, purified from placenta, was taken up from the culture medium by skin fibroblasts from patients with fucosidosis (alpha-L-fucosidase deficiency). The rate of uptake was low (uptake coefficient = 6 X 10(-4) ml.mg-1.h-1). Intracellular alpha-L-fucosidase activity was directly proportional to enzyme in the medium up to an activity of at least 40 nmoles/min/ml. No evidence for saturation of specific cell-surface receptors was seen. However, uptake was reduced by 75% by 1 mM mannose-6-phosphate and by 50% by 1mM glucose-6-phosphate, suggesting that uptake may be mediated by a receptor recognising a phosphorylated sugar or an analagous compound. Enzyme taken up by the cells was most active in subcellular fractions enriched with lysosomes and had an isozyme pattern, by isoelectric focusing, identical to that of the original enzyme preparation. Fucosidosis fibroblasts were shown to accumulate low molecular-weight, fucose-containing compounds to a level several times greater than control cells. This stored material was eluted from Sephadex G-25 as an asymmetrical peak with an elution volume of approximately twice the void volume of the column. Addition of placental alpha-L-fucosidase to the culture medium of fucosidosis fibroblasts prevented excessive accumulation of fucose-containing material and accelerated the breakdown of material accumulated prior to enzyme uptake.

Urinary abnormalities in fucosidosis. Characterization of a disaccharide and two glycoasparagines

The urinary excretion of fucose-containing material was found to be highly increased in a patient with fucosidosis type 2. Three structurally related compounds, a disaccharide and two glycoasparagines, were isolated from the urine. The isolation procedure included ultrafiltration, gel chromatography on Sephadex G-25, preparative zone electrophoresis and paper chromatography. From structural studies including optical rotation, sugar analysis, methylation analysis, ninhydrin degradation, reduction with lithium aluminium hydride and partial hydrolysis, the following structures were deduced: formula (see text), where Fucp is fucopyranose, Manp is mannopyranose, Galcp is galactopyranose, GlcNAcp is 2-acetamido-2-deoxyglucopyranose and Asn is asparagine. The yields of these compounds were 1.7, 40, and 6 mg/l, respectively. The origin of the disaccharide and the two glycoasparagines is probably the core region of glycoprotein carbohydrate chains.

Alpha-L-fucosidase in cultured bone marrow fibroblasts from fucosidosis patients

Bone marrow fibroblasts were cultured from two patients with fucosidosis type 2, six control subjects, and three patients with other lysosomal disorders. Optimal conditions for measuring alpha-L-fucosidase activity in lysates of these cells with the fluorogenic substrate 4-methylumbelliferyl-alpha-L-fucoside were established. The pH profile of normal bone marrow fibroblasts showed three peaks and a shoulder of enzymatic activity, with maximum activity at pH 4.75. In cells derived from fucosidosis patients two peaks of apparent alpha-L-fucosidase activity were obtained; the pH optimum was 4.5. alpha-L-Fucosidase activity (mean +/- SD) in the fucosidosis and control bone marrow fibroblasts was 2.5 and 312.4 +/- 10.9 nmoles 4-methylumbelliferone per milligram protein per hour, respectively. A reduction in the apparent specific enzymatic activity in the fucosidosis cells was observed by using increasing concentrations of cellular protein in the assay system. Mixing experiments between normal and fucosidosis cells gave the expected activities. These findings indicate that cultured bone marrow fibroblasts can be used for the diagnosis and study of fucosidosis.

Histomorphologic and histochemical investigations in mannosidosis. A light and electron microscopic study

Morphologic and histochemical studies have been performed at light and electron microscopic level on needle-liver biopsy specimens, circulating blood lymphocytes and fibroblast cultures from patients with mannosidosis. The findings demonstrated generalized storage phenomena of varying degrees in the various tissues examined. Histochemical findings were in agreement with the biochemical nature of the stored material. Enzyme histochemical methods indicated storage in the lysosomes, at least in the hepatocytes. The ultrastructural appearance of mannosidosis in itself has but a limited diagnostic significance since the morphology and distribution of vacuoles have characteristics in common with other storage diseases. Repeated liver biopsy disclosed extensive storage in the hepatic tissue. However, the progression of the disease was not accompanied by severe mechanical destruction or microcirculatory disturbances.

Uptake of iodinated human kidney alpha-D-mannosidase by rat liver- Association with membrane elements and stability in vivo and in vitro

1. Human kidney alpha-D-mannosidase (form A) was labelled with 125I to a specific radio-activity of approx. 2250muCi/mg of protein, essentially without loss of enzymic activity. The enzymic activity and radioactivity of the iodinated material also co-migrated in gel filtration and gel electrophoresis. 2. The binding of 125I-labelled mannosidase in vitro to particulate material in liver and kidney homogenates was of the other of 2 pg/mg of particulate material in liver and kidney homogenates was of the order of 2pg/mg of particulate protein withing 16h at 37 degrees C, and essentially zero in intervals of up to 60 min. The degradation in vitro of labelled exogenous mannosidase was of the order of 10-20pg/ 16th per mg of protein in postnuclear supernatant, and it was saturated entirely within 1h at 37 degrees C. 3. The binding of labelled mannosidase in vivo to particulate elements of liver homogenates 60 min after intravenous injection was at least 10 times higher in terms of specific radioactivity than the highest value attainable in vitro. Virtually all exogenous enzyme bound to liver particulate material could be recovered in macromolecular form after disruption of membranes by detergents. 4. The radioactive enzyme bound to liver particulate material could be detached almost completely by shearing, repeated freezing and thawing, and exposure to strong detergents under conditions that do not eliminate rough-endoplasmic-membrane structure. It could bot be released, however, by high salt concentration (0.5M-KC1) or by exposure to weak detergents such as Tween 80. The particle-bound enzyme should thus be associated with plasma membranes and lysosome-like elements. 5. Of the rat tissues studied, only liver could approach, within 60 min after the injection, the concentration of exogenous mannosidase found in the blood serum. The activity per g tissue weight fell progressively from liver (60% of serum value) to kidney (16% of serum value), lung (8% of serum vlaue), spleen (6% of serum value) and brain (0.9% of serum value). Most of the radioactive enzyme found in tissues other than liver appeared to be present in a free form, whereas in liver more than 50% of the labelled enzyme was associated with membrane elements.

Cultured fucosidosis fibroblasts: a simple technique demonstrating storage of tritiated-fucose labeled material

Incorporation of tritiated fucose into the acid-soluble and acid-insoluble fractions of cultured fucosidosis and control fibroblast monolayers was determined over a 10-day period. Fucosidosis cells incorporated significantly more label into the acid-soluble, but not the acid-insoluble fraction, than control cells. The ratio of acid-insoluble radioactivity increased lineraly from 1 to 10 days for the fucosidosis cells, indicating the storage of low molecular weight partial degradation products.

Storage of mannose-containing material in cultured human mannosidosis cells and metabolic correction by pig kidney alpha-mannosidase

Skin fibroblasts from healthy individuals and a mannosidosis patient were cultured in the presence of [2-3H] mannose and the cell homogenates were fractionated by trichloroacetic acid precipitation into a precipitable and a non-precipitable portion. In uptake as well as in chase experiments the precipitable fractions show no significant difference in their content of radioactivity, while an increased level of radioactivity is found in the non-precipitable fraction of mannosidosis cells. This higher radioactivity content is due to a higher mannose content and is caused by a slower degradation of this fraction. The differences between the metabolisms of the two cell lines can be expressed by the ratio of radioactivity in the non-precipitable and the precipitable fractions. This value is about three times higher for mannosidosis than for control cells. Pig kidney alpha-mannosidase is taken up by both cell lines and is able to correct the impaired degradation of the non-precipitable material in mannosidosis cells, as shown by the normalization of the above defined ratio of radioactivity for this cell type.

Human alpha-fucosidase. Single residual enzymatic form in fucosidosis

Four major forms of alpha-fucosidase (EC 3.2.1.51) activity were separated by isoelectrofocusing from sera of normal control individuals. All forms shifted towards less acidic pI values after neuraminidase treatment. In two patients affected with fucosidosis, only a single major acidic peak was observed and this was affected to a lesser degree by neuraminidase treatment. The kinetics of heat inactivation of the residual activity found in these two patients showed two decay rates while the controls showed only one rate. These data are considered in relation to the hypothesis of the existence of interconvertible thermolabile and thermostable forms of the enzyme which has been discussed in the preceeding paper. The residual alpha-fucosidase found in patients could be structurally altered so that its ability to form the thermostable higher molecular weight aggregates is impaired.