Newborn screening for mucopolysaccharidoses: a pilot study of measurement of glycosaminoglycans by tandem mass spectrometry

BACKGROUND

Mucopolysaccharidoses (MPS) are a group of inborn errors of metabolism that are progressive and usually result in irreversible skeletal, visceral, and/or brain damage, highlighting a need for early diagnosis.

METHODS

This pilot study analyzed 2862 dried blood spots (DBS) from newborns and 14 DBS from newborn patients with MPS (MPS I, n = 7; MPS II, n = 2; MPS III, n = 5). Disaccharides were produced from polymer GAGs by digestion with chondroitinase B, heparitinase, and keratanase II. Heparan sulfate (0S, NS), dermatan sulfate (DS) and mono- and di-sulfated KS were measured by liquid chromatography tandem mass spectrometry (LC-MS/MS). Median absolute deviation (MAD) was used to determine cutoffs to distinguish patients from controls. Cutoffs were defined as median + 7× MAD from general newborns.

RESULTS

The cutoffs were as follows: HS-0S > 90 ng/mL; HS-NS > 23 ng/mL, DS > 88 ng/mL; mono-sulfated KS > 445 ng/mL; di-sulfated KS > 89 ng/mL and ratio di-KS in total KS > 32 %. All MPS I and II samples were above the cutoffs for HS-0S, HS-NS, and DS, and all MPS III samples were above cutoffs for HS-0S and HS-NS. The rate of false positives for MPS I and II was 0.03 % based on a combination of HS-0S, HS-NS, and DS, and for MPS III was 0.9 % based upon a combination of HS-0S and HS-NS.

CONCLUSIONS

Combination of levels of two or more different GAGs improves separation of MPS patients from unaffected controls, indicating that GAG measurements are potentially valuable biomarkers for newborn screening for MPS.

Anti-atherosclerotic effect of microbial hyaluronate lyase from group B streptococci

The effect of the microbial hyaluronic acid splitting enzyme hyaluronate lyase produced by Streptococcus agalactiae was investigated in vitro in human atherosclerotic plaque specimens and in vivo on Watanabe heritable hyperlipidaemic rabbits (WHHL) as an animal model for familiar hypercholesteraemia. The in vitro presence of the enzyme caused a partial destruction of the atherosclerotic plaque surfaces as well as releasing of glucuronic acid and solid calcium-containing materials from pieces of atherosclerotic plaques in human arteries. Accordingly hyaluronic acid seems to be the main component for anchoring of calcium deposits on the plaque surfaces. Repeated intravenous injections of hyaluronate lyase in WHHL rabbits resulted in a tendency of decreased formation of atherosclerotic plaques. The observed effects are discussed to be primary the result of the splitting of hyaluronic acid in the vessels.

Evaluation of coagulation during cardiopulmonary bypass with a heparinase-modified thromboelastographic assay

Thromboelastography (TEG) is a useful method of assessing perioperative coagulation function in patients undergoing cardiac surgery. The presence of significant amounts of heparin in blood samples, however, prevents determination of changes in coagulation function by TEG or introduces artifactual error if samples contain heparin that is not present in vivo. For these reasons, whole blood coagulation function monitoring with TEG has not been feasible during cardiopulmonary bypass (CPB) with heparin anticoagulation. In this study, data obtained from 42 volunteers are presented to describe the effects of heparinase on TEG variables in the presence and absence of heparin. These data indicate that heparinase does not affect TEG parameters of whole blood not containing heparin and reverses the TEG effects of low levels of heparin contamination. Subsequently, 51 patients undergoing coronary artery surgery were studied using a modified TEG assay that incorporates in vitro application of heparinase to allow measurement of TEG parameters before, during, and after CPB. Heparinase-modified TEG assays facilitated diagnosis of heparin contamination in preoperative blood samples and permitted baseline TEG evaluation in patients receiving preoperative heparin infusions. Heparinase-modified TEG assays revealed declines in alpha and MA values during CPB, which persisted and significantly correlated with values after protamine infusion (alpha: r = 0.77, P = 0.001; MA: r = 0.78, P = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of immobilized heparinase in human blood

Immobilized enzyme reactors can form the basis of useful blood detoxification systems. One such reactor was developed for heparin neutralization by immobilized heparinase. In this article, reactor kinetics were studied under clinically relevant conditions. Heparin neutralization was assessed in vitro in whole human blood using (a) a well-mixed batch reactor, and (b) an oscillating, continuous-flow reactor. The kinetics of heparin neutralization in human blood were first order over the entire range of heparin and enzyme concentrations and particle fractions tested. The kinetic rate was not sensitive to physiological variations in the concentration of antithrombin, a heparin binding protein in blood. Enzyme activity did not decrease significantly over the 2 hour test period. Kinetic control of the system with minimal intraparticle diffusional limitations was suggested by the Thiele moduli (0.11-0.67) and effectiveness factors (0.98 +/- 0.01). The ratio kcat/Km obtained in batch studies was 0.0028 +/- 0.0008 cm3/microgram-min. A continuous-flow oscillating reactor within a closed recirculation loop performed as a single well mixed batch reactor; there was a short mixing time of recirculating blood when compared to reaction time. A model based on this mixing pattern and the kinetics obtained in independent batch studies accurately predicted heparin neutralization profiles observed in the continuous-flow system.

Activation of platelet heparitinase by tumor cell-derived factors

The nature of the cooperation between platelets and tumor cells during the process of blood-borne metastasis is essentially unknown. In previous in vitro studies we showed that platelets participated in the formation of gaps in the endothelial cell lining, and that concomitantly heparan sulfate glycosaminoglycans were degraded by the platelet heparitinase, released on activation of platelets. In the current study we show that the ability to degrade proteoheparan sulfate derived from endothelial extracellular matrix is gradually eliminated when the number of human platelets is decreased from 5 x 10(7) to 10(6) cells/mL. When aliquots of conditioned media or lysates of either Eb or heat-inactivated ESb mouse lymphoma cells (both of which showed no heparanase activity) were added to freeze-thawed lysates of 10(6) platelets, a reappearance of platelet heparitinase activity was observed. A similar activation was not elicited by lysates of several normal mammalian cells. These data suggest that in its native form, a fraction of the platelet heparitinase is stored in an inactive form that can be activated by a factor secreted by lymphoma, but not by normal cells. Partial characterization of the heparitinase-activating factor showed that it is a heat-stable polyanionic molecule, devoid of proteolytic activity and resistant to both proteolytic and chondroitinase digestions. Activation of platelet heparitinase was also observed on coincubation with chondroitinases ABC and AC, suggesting that the inactive form of platelet heparitinase could result from a complex formation with a chondroitinase-sensitive proteoglycan. The lymphoma-derived heparitinase activating factor itself is, however, not a chondroitinase, because activity of chondroitinase could not be detected in Eb and ESb cells. A possible mechanism by which tumor cells recruit and regulate the activity of platelet heparitinase, and its relevance to the progression of blood borne metastasis, is discussed.

Characterization of a heparin-like activity released in dogs during deep hypothermia

In a previous paper, we demonstrated that deep hypothermia in dogs provokes a release of a heparin-like factor. In the present study, we investigated some properties of this anticoagulant activity and compared it with exogenous heparin activity. The endogenous anticoagulant inhibited factors IIa and Xa; it was hydrolysed by heparinase and was AT III dependent. However, it differed from heparin in so far as it was adsorbed on cation exchange gel at neutral pH, its inhibition was decreased in the presence of neuraminidase, and it could not be neutralized with Polybrene or protamine. A release of heparan sulphate is suggested but remains to be demonstrated.

Monocyte activating factor in sarcoidosis. I. Existence of the factor in sarcoidosis sera

Sarcoidosis sera were found to have the ability to induce normal human monocytes to spread. Gel filtration of sarcoidosis sera on Sephadex G-200 showed that the factor mainly responsible for this activity had a molecular weight of about 70,000. The spreading factor also possessed the ability to increase all cell size of normal human monocytes as well as to increase their phagocytosis and glucose consumption. Accordingly, the spreading factor seems to be considered as a monocyte activating factor. Sarcoidosis sera showed a macrophage migration inhibitory activity, as well. On Sephadex G-200 column chromatography of the sera, the most obvious inhibitory activity was eluted in the fraction with a molecular weight of about 45,000. The macrophage migration inhibitory factor had the ability neither to increase cell size of normal human monocytes nor to increase their phagocytosis and glucose consumption.

Effects of fibronectin-related peptides on cell spreading

Four synthetic peptides related in amino acid sequence to the area of the fibronectin molecule thought to be involved in cell binding were tested for the ability to inhibit cell spreading promoted by several different attachment factors. Effects of the peptides were assayed on a number of cell types. For all cell types tested, peptides effective at inhibiting fibronectin-promoted cell spreading were found also to inhibit cell spreading promoted by human serum spreading factor (SF). These peptides were also capable of inhibiting to a lesser extent cell spreading promoted by other attachment factors, although this phenomenon was dependent on the cell type examined.

Degradation of sulfated proteoglycans in the subendothelial extracellular matrix by human platelet heparitinase

Cultured vascular and corneal endothelial cells produce an underlying extracellular matrix (ECM) which induces platelet adherence, aggregation, and release reaction. Incubation of a metabolically (35S)O = 4-labeled ECM with platelet-rich plasma or washed platelets, but not with platelet-poor plasma, resulted in degradation of its heparan sulfate-containing proteoglycans into labeled fragments four to five times smaller than intact glycosaminoglycan side chains. These fragments were sensitive to deamination with nitrous acid and were not produced in the presence of heparin, indicating that heparan sulfate in the ECM is susceptible to cleavage by the platelet heparitinase. This degradation required adhesion of platelets to the ECM rather than aggregation since it was not inhibited by aspirin, which prevented platelet aggregation but not adherence. The enzyme was not released during aggregation of platelets on the ECM but was readily liberated upon their exposure to thrombin. This liberation was inhibited in the presence of prostacyclin (PGI2). Isolated high molecular weight proteoglycans first released from the ECM by incubation with platelet poor plasma served as a substrate for further degradation by the platelet heparitinase, suggesting a cascade mechanism for degradation of heparan sulfate in the ECM. Heparitinase, although to a lower level, was also active when washed platelets were added on top of a confluent endothelial cell monolayer covering the (35S)O = 4-labeled ECM. It is suggested that the platelet heparitinase may be involved in the impairment of the integrity of the vessel wall and thus facilitate the extravasation of blood-borne cells.

Quantitation of spreading factor in human biologic fluids

Spreading factor (SF) is a glycoprotein isolated from human plasma or serum that promotes attachment and spreading of a wide variety of mammalian cells in culture. Under appropriate conditions, this factor also affects cell proliferation and differentiation in vitro. An immunoassay employing a previously characterized monoclonal antibody to SF, with purified SF as a reference standard, was utilized to quantitate levels of SF in human plasma, serum, amniotic fluid, and urinary protein. Specific anti-SF monoclonal antibody-binding activities in individual samples of human serum were identical to specific anti-SF monoclonal antibody-binding activities in the plasma samples from which the sera were derived. Specific anti-SF monoclonal antibody-binding activity in plasma from adults, when compared with purified SF reference standards, represented an average of 4 micrograms of SF per mg plasma protein (range, 2.5 to 7 micrograms/mg). Specific anti-SF monoclonal antibody-binding activity in sera from fetal cord blood, infants, children, or adolescents was not significantly different from that of adults. Specific anti-SF monoclonal antibody-binding activities in amniotic fluid samples from pregnancies of 12 to 23 weeks' gestation were within the range observed in sera of adults. Anti-SF monoclonal antibody-binding activity in concentrated urinary protein, when compared with purified SF reference standards, represented a specific activity of 10.9 micrograms of SF per mg protein.

Isolation of human serum spreading factor

Serum spreading factor (SF) was isolated from human serum by a four-step procedure employing affinity chromatography on glass beads, concanavalin A-Sepharose, DEAE-agarose, and heparin-agarose. The final product was purified approximately 260-fold from the starting material and was maximally active in assays of cell spreading-promoting activity at 300 ng/ml. The isolated human SF preparation consisted of two proteins of apparent molecular weights approximately 65,000 (SF65) and 75,000 (SF75). Both SF65 and SF75 have been shown previously to exhibit cell spreading-promoting activity and to bind monoclonal antibody to human serum SF.

Purification and properties of human platelet heparitinase

An endoglycosidase which cleaves heparin and heparan sulfate was isolated from outdated human platelets by freeze-thaw solubilization, heparin-Sepharose chromatography, DEAE-cellulose chromatography, hydroxylapatite chromatography, octyl-agarose chromatography, concanavalin A-Sepharose chromatography, and Sephacryl S-200 gel filtration. The overall extent of purification of the platelet heparitinase is about 240,000-fold and the overall yield of the enzyme is about 5.6% as compared to the initial freeze-thaw solubilization preparation. The final product is physically homogeneous as judged by disc gel electrophoresis at acidic pH as well as gel filtration chromatography and exhibits an apparent molecular weight of approximately 134,000. Furthermore, our results indicate that the above enzyme is present within platelet lysosomes. The biologic potency of the endoglycosidase was examined as a function of pH. The data show that the platelet heparitinase is maximally active from pH 5.5 to pH 7.5. However, the enzyme possesses minimal ability to cleave heparin at pH less than 4.0 or greater than 9.0. The substrate specificity of the platelet endoglycosidase was determined by identifying susceptible linkages within the heparin molecule that can be cleaved by the above component. Our studies indicate that this enzyme is only able to hydrolyze glucuronsylglucosamine linkages. Furthermore, investigation of the structure of the disaccharide which lies on the nonreducing end of the cleaved glucuronic acid residue suggests that N-sulfation of the glucosamine moiety or ester sulfation of the adjacent iduronic acid groups are not essential for bond scission.

Inhibition of vascular smooth muscle cell growth by endothelial cell-derived heparin. Possible role of a platelet endoglycosidase

Bovine aortic endothelial cells release a heparin-like substance in the presence of 0.4% fetal calf serum. This substance inhibited the growth of smooth muscle cells in vitro by about 70%. Substitution of platelet-poor plasma for serum resulted in minimal liberation of inhibitory activity from the cells unless at least 10-fold higher concentrations of platelet-poor plasma were utilized. This suggested that a platelet product was involved in the release process. Therefore, we examined the ability of the platelet heparitinase described in the preceding communication to release heparin-like species from cultured endothelial cells. Our results show that when endothelial cells were exposed to serum-free medium containing 1 ng/ml of the purified platelet endoglycosidase, at least as much inhibitory activity was released as was obtained with 0.4% serum. Dose response experiments indicated that only 10 pg/ml of the enzyme were necessary to liberate 50% of the inhibitory activity from endothelial cells. The heparin-like nature of the inhibitory substance was demonstrated by its sensitivity to Flavobacterium heparinase. Utilizing appropriate controls, the release of heparin-like material by the endoglycosidase was shown to be enzyme-specific and was not due to artifacts of experimental manipulations. In addition, this enzyme did not convert prereleased material to an active component, but directly liberated the active heparin-like species from endothelial cells. A simple model describing the possible role of heparin-like components and the endoglycosidase in the normal and injured wall is presented.

Characterization of a platelet endoglycosidase degrading heparin-like polysaccharides

An endoglycosidase (heparitinase) acting on heparin and heparan sulfate was partially purified (approximately 300 times) from human platelets by affinity chromatography on heparan sulfate substituted Sepharose. Only heparin-like polysaccharides were degraded by the enzyme. The susceptibility of various biosynthetic heparin intermediates indicated that the platelet heparitinase had a requirement for sulfamino but not ester sulfate groups. No activity toward other uronic acid containing glycosaminoglycans could be demonstrated. Glucuronidic but not glucosaminidic linkages in heparin or heparan sulfate were attacked by the enzyme as shown by analysis of the reducing sugar moiety in oligosaccharide products. The anticoagulant activity of heparin, determined in an antithrombin III activation assay, was markedly reduced after treatment with the heparitinase. The enzyme was released from its storage site in platelets after induction of the platelet release reaction. The physiological function of platelet heparitinase is not known but may be to modify extracellular heparin-like polysaccharides in the vascular system.