Recent advances on the pathogenesis of Huntington's disease

We review recent advances regarding the pathogenesis of Huntington's disease (HD). This genetic neurodegenerative disorder is caused by an expanded CAG repeat in a gene coding for a protein, with unknown function, called huntingtin. There is selective death of striatal and cortical neurons. Both in patients and a transgenic mouse model of the disease, neuronal intranuclear inclusions, immunoreactive for huntingtin and ubiquitin, develop. Huntingtin interacts with the proteins GAPDH, HAP-1, HIP1, HIP2, and calmodulin, and a mutant huntingtin is specifically cleaved by the proapoptotic enzyme caspase 3. The pathogenetic mechanism is not known, but it is presumed that there is a toxic gain of function of the mutant huntingtin. Circumstantial evidence suggests that excitotoxicity, oxidative stress, impaired energy metabolism, and apoptosis play a role.

Early sac shrinkage predicts a low risk of late complications after endovascular aortic aneurysm repair

BACKGROUND

Aneurysm shrinkage has been proposed as a marker of successful endovascular aneurysm repair (EVAR). Patients with early postoperative shrinkage may experience fewer subsequent complications, and consequently require less intensive surveillance.

METHODS

Patients undergoing EVAR from 2000 to 2011 at three vascular centres (in 2 countries), who had two imaging examinations (postoperative and after 6-18 months), were included. Maximum diameter, complications and secondary interventions during follow-up were registered. Patients were categorized according to early sac dynamics. The primary endpoint was freedom from late complications. Secondary endpoints were freedom from secondary intervention, postimplant rupture and direct (type I/III) endoleaks.

RESULTS

Some 597 EVARs (71.1 per cent of all EVARs) were included. No shrinkage was observed in 284 patients (47.6 per cent), moderate shrinkage (5-9 mm) in 142 (23.8 per cent) and major shrinkage (at least 10 mm) in 171 patients (28.6 per cent). Four years after the index imaging, the rate of freedom from complications was 84.3 (95 per cent confidence interval 78.7 to 89.8), 88.1 (80.6 to 95.5) and 94.4 (90.1 to 98.7) per cent respectively. No shrinkage was an independent risk factor for late complications compared with major shrinkage (hazard ratio (HR) 3.11; P < 0.001). Moderate compared with major shrinkage (HR 2.10; P = 0.022), early postoperative complications (HR 3.34; P < 0.001) and increasing abdominal aortic aneurysm baseline diameter (HR 1.02; P = 0.001) were also risk factors for late complications. Freedom from secondary interventions and direct endoleaks was greater for patients with major sac shrinkage.

CONCLUSION

Early change in aneurysm sac diameter is a strong predictor of late complications after EVAR. Patients with major sac shrinkage have a very low risk of complications for up to 5 years. This parameter may be used to tailor postoperative surveillance.

Lack of an effective drug therapy for abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) rupture is a common cause of death in adults. Current AAA treatment is by open surgical or endovascular aneurysm repair. Rodent model and human epidemiology, and genetic and observational studies over the last few decades have highlighted the potential of a number of drug therapies, including medications that lower blood pressure, correct dyslipidaemia, or inhibit thrombosis, inflammation or matrix remodelling, as approaches to managing small AAA. This review summarizes prior AAA pathogenesis data from animal and human studies aimed at identifying targets for the development of drug therapies. The review also systematically assesses past randomized placebo-controlled drug trials in patients with small AAAs. Eleven previously published randomized-controlled clinical trials testing different drug therapies aimed at slowing AAA progression were identified. Five of the trials tested antibiotics and three trials assessed medications that lower blood pressure. Meta-analyses of these trials suggested that neither of these approaches limit AAA growth. Allocation to blood pressure-lowering medication was associated with a small reduction in AAA rupture or repair, compared to placebo (relative risk 0.94, 95% confidence intervals 0.89, 1.00, P = 0.047). Three further trials assessed the effect of a mast cell inhibitor, fibrate or platelet aggregation inhibition and reported no effect on AAA growth or clinical events. Past trials were noted to have a number of design issues, particularly small sample sizes and limited follow-up. Much larger trials are needed to properly test potential therapeutic approaches if a convincingly effective medical therapy for AAA is to be identified.

Novel aspects of glypican glycobiology

Mutations in glypican genes cause dysmorphic and overgrowth syndromes in men and mice, abnormal development in flies and worms, and defective gastrulation in zebrafish and ascidians. All glypican core proteins share a characteristic pattern of 14 conserved cysteine residues. Upstream from the C-terminal membrane anchorage are 3-4 heparan sulfate attachment sites. Cysteines in glypican-1 can become nitrosylated by nitric oxide in a copper-dependent reaction. When glypican-1 is exposed to ascorbate, nitric oxide is released and participates in deaminative cleavage of heparan sulfate at sites where the glucosamines have a free amino group. This process takes place while glypican-1 recycles via a nonclassical, caveolin-1-associated route. Glypicans are involved in growth factor signalling and transport, e.g. of polyamines. Cargo can be unloaded from heparan sulfate by nitric oxide-dependent degradation. How glypican and its degradation products and the cargo exit from the recycling route is an enigma.

Structural characterization of a novel xylolipid biosurfactant from Lactococcus lactis and analysis of antibacterial activity against multi-drug resistant pathogens

Control of emerging multi-drug resistant bacteria is one of the major prerequisite in the management of opportunistic infections. Current research is focused towards the identification of effective control agents from biological origin without any alarming side effects. Lactococcus lactis, probiotic organisms was isolated and purified biosurfactant from the bacteria exhibited surface active and emulsification activities comparable to the standard biosurfactant producing bacteria Bacillus licheniformis MTCC 429. Co-culturing of the isolate with the standard organism increased the biosurfactant production and surfactant activity. Biosurfactant from the L. lactis was characterized as glycolipids which consist of Methyl-2-O-methyl-beta-d-xylopyranoside with octadecanoic acid with a cumulative molecular weight of approximately 476g/mol by GC-MS and NMR studies. Purified biosurfactants showed broad range of antibacterial activity and are safe to administrate orally and dermally. So it could be used as a therapeutic agent in pharmaceutical or as a preservative in food industries.

Changes in the management of infrarenal abdominal aortic aneurysm disease in Sweden

Background

Treatment of abdominal aortic aneurysm (AAA) has changed over time, with endovascular repair (EVAR) being the main technical revolution. This study assessed the effect of this change on outcome on a national basis over a 17-year interval.

Methods

Primary infrarenal AAA repairs in Swedish residents aged 50 years and older, in the Swedish Vascular Registry (Swedvasc) 1994–2010, were analysed. The rate per 100 000 population, patient characteristics, operative technique and outcome were assessed for the intervals 1994–1999, 2000–2005 and 2006–2010.

Results

Some 11 336 intact aneurysm repairs were performed. The overall rate per 100 000 increased (18·4 in 1994–1999, 19·4 in 2000–2005 and 24·0 in 2006–2010; P &lt; 0·001), most noticeably among older people (18 per cent increase among those aged 50–64 years, P = 0·004; 27 per cent in 65–79-year-olds, P &lt; 0·001; 128 per cent in those aged at least 80 years, P &lt; 0·001). The use of EVAR increased rapidly after 2005 (rate: 0·6 in 1994–1999, 4·4 in 2000–2005 and 11·8 in 2006–2010; P &lt; 0·001). The 30-day mortality rate decreased after open repair (4·7, 3·4 and 2·7 per cent respectively; P &lt; 0·001), but was stable after EVAR (2·6, 2·2 and 1·6 per cent; P = 0·227). Some 4972 ruptured aneurysm (rAAA) repairs were performed. The rate decreased after 2005 (9·3 in 1993–1999, 9·3 in 2000–2005 and 8·4 in 2006–2010; P = 0·006). The use of EVAR for rAAA increased over time (rate: 0, 0·5 and 1·6 respectively; P &lt; 0·001), whereas open repair decreased (9·3, 8·8 and 6·8; P &lt; 0·001). Thirty-day mortality decreased over time (38·3, 32·8 and 28·4 per cent; P &lt; 0·001).

Conclusion

The introduction of EVAR has been associated with an increased number of intact AAA repairs, which has accelerated recently, whereas the rate of rAAA repair has started to decline. Simultaneously, outcomes have improved.

Editor's Choice - Trend-break in Abdominal Aortic Aneurysm Repair With Decreasing Surgical Workload

BACKGROUND

The epidemiology and management of abdominal aortic aneurysms (AAAs) has changed drastically in the past decades, with implementation of nationwide screening programs, introduction of endovascular repair (EVAR), and reduced prevalence of the disease. This report aims to assess recent trends in AAA repair epidemiology in Sweden in this context.

METHODS

Primary AAA repairs registered in the nationwide Swedish Vascular Registry (Swedvasc) 1994-2014 were analyzed regarding patient characteristics, repair incidence, technique, and outcome. Four time periods were compared: 1994-1999, 2000-2004, 2005-2009, and 2010-2014.

RESULT

The incidence of intact AAA repair increased (18.4/100,000 1994-1999, 27.3/100,000 2010-2014, p < .001) predominantly among octogenarians (12.7/100,000 1994-1999, 36.0/100,000 2010-2014, p < .001). The utilization of EVAR increased (58% of all intact AAA repairs 2010-2014), especially among octogenarians (80% 2010-2014). During the last time period, however, the incidence of intact AAA repair stabilized, despite an increasing number of screening-detected AAAs operated on (19% in 2010-2014). Short- and long-term outcome after intact AAA repair continued to improve, most pronounced among octogenarians (30-day mortality 9% 1994-1999, 2% 2010-2014, p < .001). The incidence of ruptured AAA repair steadily decreased (9.2/100,000 1994-1999, 6.9/100,000 2010-2014, p < .001) and the use of EVAR for ruptures increased (30% in 2010-2014). The previously observed improvement of short- and long-term outcome after ruptured AAA repair (30-day mortality 38% 1994-1999, 28% 2010-2014, p < .001) stalled during the last time period. The overall 30-day mortality after ruptured AAA repair was 22% after EVAR versus 31% after open repair in 2010-2014. The corresponding mortality for octogenarians was 28% versus 42%.

CONCLUSIONS

For the first time, a halt in intact AAA repair workload could be identified. This trend-break occurred despite continued increase in treatment of octogenarians and screening-detected aneurysms. Additionally, the ruptured AAA repair incidence continued to decrease. These findings, together with the sustained improvement in survival after AAA repair, may have important impact on planning of vascular surgical services.

Osteosarcoma of the jaw bones

Osteosarcoma of the jaw bone is comparatively rare and accounts for about 6.5% of all osteosarcomas. We treated eight cases of osteosarcoma of the jaw bone involving the mandible and maxilla in equal proportions between 1986-1992. The median age was 31 years and male: female ratio was 5:3. Swelling and bony expansion were the most common presentations. Radiologically six patients had lytic lesions, and histopathologically they were osteoblastic (n = 4), chondroblastic (n = 3) and fibroblastic (n = 1). Three patients, two with mandibular and one with maxillary osteosarcoma underwent radical surgery and six courses of cisplatinum-based chemotherapy. All were alive and disease free 24, 30, and 54 months after treatment. Histologically all three were chondroblastic. Five patients had incomplete or palliative treatment. All patients died of progressive or locally recurrent disease within 2 years.

Biosynthesis of decorin and glypican

Decorin and glypican are two examples of exclusively chondroitin/dermatan sulfate and heparan sulfate-substituted proteoglycans, respectively. Decorin is a secretory product, whereas glypican is linked to membrane lipids via a glycosyl-phosphatidyl-inositol (GPI) anchor. The nascent decorin protein enters the lumen of the ER, whereas that of glypican is transferred to the preformed GPI-anchors. Both types of glycosaminoglycuronans are initiated on Ser residues located in special consensus sequences, and the first glycosylation steps constitute a common pathway: the generation of the linkage region GlcA-Gal-Gal-Xyl-Ser<. The nature of the enzymes involved will be reviewed with special emphasis on the recently discovered transient 2-phosphorylation of xylose. The initiation enzymes (betaGalNAc-T1 and alphaGlcNAc-T1) then use these tetrasaccharide primers for either chondroitin or heparan sulfate assembly. The selection mechanism is not yet fully understood. The transferases that form the linkage-region and add the first hexosamine, as well as the uronosyl C-5 epimerases, appear to be products of single genes, but many isoforms of the copolymerases and sulfotransferases forming the repetitive part of the glycan chains are currently being discovered. When these enzymes work together, the fine structure of the glycosaminoglycuronans appears to be generated through the selective expression of isoforms that only operate in certain structural contexts. During heparan sulfate assembly, generation of GlcNH(2) as a permanent feature is now well recognised. Studies on glypican-1 glycoforms that recycle suggest that heparan sulfate chains are degraded by endoheparanase at or near GlcNH(2) residues, followed by deaminative cleavage catalysed by NO-derived nitrite. Chain-truncated glypican-1 can serve as a precursor for the reformation of a proteoglycan with full-size chains. Regulation of biosynthesis can be exercised at several levels, such as expression of the core protein, selection for chondroitin or heparan sulfate assembly, expression of modifying enzymes, and degradation and remodelling. Cytokines, growth factors, NO and polyamines may have regulatory roles.

Modulations of glypican-1 heparan sulfate structure by inhibition of endogenous polyamine synthesis. Mapping of spermine-binding sites and heparanase, heparin lyase, and nitric oxide/nitrite cleavage sites

Cell surface heparan sulfate proteoglycans facilitate uptake of growth-promoting polyamines (Belting, M., Persson, S., and Fransson, L.-A. (1999) Biochem. J. 338, 317-323; Belting, M., Borsig, L., Fuster, M. M., Brown, J. R., Persson, L., Fransson, L.-A., and Esko, J. D. (2001) Proc. Natl. Acad. Sci. U. S. A., in press). Here, we have analyzed the effect of polyamine deprivation on the structure and polyamine affinity of the heparan sulfate chains in various glypican-1 glycoforms synthesized by a transformed cell line (ECV 304). Heparan sulfate chains of glypican-1 were either cleaved with heparanase at sites embracing the highly modified regions or with nitrite at N-unsubstituted glucosamine residues. The products were separated and further degraded by heparin lyase to identify sulfated iduronic acid. Polyamine affinity was assessed by chromatography on agarose substituted with the polyamine spermine. In heparan sulfate made by cells with undisturbed endogenous polyamine synthesis, free amino groups were restricted to the unmodified, unsulfated segments, especially near the core protein. Spermine high affinity binding sites were located to the modified and highly sulfated segments that were released by heparanase. In cells with up-regulated polyamine uptake, heparan sulfate contained an increased number of clustered N-unsubstituted glucosamines and sulfated iduronic acid residues. This resulted in a greater number of NO/nitrite-sensitive cleavage sites near the potential spermine-binding sites. Endogenous degradation by heparanase and NO-derived nitrite in polyamine-deprived cells generated a separate pool of heparan sulfate oligosaccharides with an exceptionally high affinity for spermine. Spermine uptake in polyamine-deprived cells was reduced when NO/nitrite-generated degradation of heparan sulfate was inhibited. The results suggest a functional interplay between glypican recycling, NO/nitrite-generated heparan sulfate degradation, and polyamine uptake.

Vitamin D nutritional status of exclusively breast fed infants and their mothers

BACKGROUND

Vitamin D nutrition has a profound effect on the development of an infant. Vitamin D status of mothers and their infants are closely correlated. While hypovitaminosis D has emerged as a significant public health problem across all age groups, there is limited information of this condition in lactating mothers and their breast fed infants.

AIM

To evaluate the vitamin D status of lactating mothers and their breast fed infants.

SUBJECTS AND METHODS

180 healthy lactating mothers and exclusively breast fed infants, 2-24 weeks old, were recruited for the study. The mother-infant pairs underwent concurrent clinical, biochemical and hormonal evaluation for calcium-vitamin D-PTH axis.

RESULTS

The mean serum 25(OH)D values in lactating mothers was 27.2 +/- 14.6 nmol/l (10.9 +/- 5.8 ng/ml), while that of their infants was 28.9 +/- 20.8 nmol/l (11.6 +/- 8.3 ng/ml). Serum 25(OH)D levels <25 nmol/l (10 ng/ml) were found in 47.8% of the mothers and 43.2% of the infants. Among these, elevated PTH levels (>54 pg/ml) were seen in 59.3% of the mothers and 69.6% of the infants. A highly significant negative correlation was found between serum 25(OH)D and PTH in mothers (r = -0.480, p = 0.01) and their infants (r = -0.431, p = 0.01). A strong positive correlation was seen of 25(OH)D levels in mother-infant pairs (r = 0.324, p = 0.001).

CONCLUSIONS

A high prevalence of vitamin D deficiency was found in lactating mothers and their exclusively breast fed infants. Infants born to mothers with hypovitaminosis D had 3.8 times higher risk of developing hypovitaminosis D as compared to those born to mothers with normal vitamin D levels.

A novel role for nitric oxide in the endogenous degradation of heparan sulfate during recycling of glypican-1 in vascular endothelial cells

We show here that the endothelial cell-line ECV 304 expresses the heparan sulfate proteoglycan glypican-1. The predominant cellular glycoform carries truncated side-chains and is accompanied by heparan sulfate oligosaccharides. Treatment with brefeldin A results in accumulation of a glypican proteoglycan with full-size side-chains while the oligosaccharides disappear. During chase the glypican proteoglycan is converted to partially degraded heparan sulfate chains and chain-truncated proteoglycan, both of which can be captured by treatment with suramin. The heparan sulfate chains in the intact proteoglycan can be depolymerized by nitrite-dependent cleavage at internally located N-unsubstituted glucosamine moieties. Inhibition of NO-synthase or nitrite-deprivation prevents regeneration of intact proteoglycan from truncated precursors as well as formation of oligosaccharides. In nitrite-deprived cells, formation of glypican proteoglycan is restored when NO-donor is supplied. We propose that, in recycling glypican-1, heparan sulfate chains are cleaved at or near glucosamines with unsubstituted amino groups. NO-derived nitrite is then required for the removal of short, nonreducing terminal saccharides containing these N-unsubstituted glucosamine residues from the core protein stubs, facilitating re-synthesis of heparan sulfate chains.

Characterization of polyhydroxyalkanoates accumulated by a moderately halophilic salt pan isolate Bacillus megaterium strain H16

AIM

Characterization of polyhydroxyalkanoates (PHA) accumulated by halophilic bacteria isolated from solar salterns.

METHODS AND RESULTS

Twenty-six halophilic isolates were obtained from solar salterns of Goa, India. They were screened for accumulation of PHA by Sudan black B, Nile blue A and Nile red stains. Strains H15, H16 and H26 were selected based on their intensity of Nile blue A/Nile red fluorescence. On the basis of phenotypic and genotypic characterization, the three isolates were identified as Bacillus megaterium. Growth kinetics and polymer accumulating capacity of strain H16 were studied in E2 mineral media with 2% glucose with/without NaCl. In the absence of NaCl, strain H16 accumulated PHA to 40·0% (w/w) of cell dry weight (CDW) at 42 h of growth, whereas in presence of 5% w/v NaCl, the culture showed longer lag phase of up to 24 h and accumulated a maximum PHA of 39% (w/w) CDW at 54 h of growth. The infrared spectra of both the polymers exhibited peaks at 1733·9 cm(-1) characteristic of C=O. Scans of (1) H nuclear magnetic resonance (NMR) showed a doublet at 2·5 ppm corresponding to methylene group (-CH(2)), the signal at 5·3 ppm corresponded to methine group (-CH-), and another signal at 1·3 ppm corresponded to the methyl group (-CH(3)). Scans of (13)C NMR showed prominent peaks at 20, 40, 67-68 and 170 ppm, indicating the polymer to be homopolymer of 3-hydroxybutyrates. The polymer is stable up to a temperature of 160°C.

CONCLUSION

Three moderately halophilic isolates (strain H15, H16 and H26) capable of accumulating PHA were isolated from solar salterns of Ribandar Goa, India, and identified as B. megaterium based on phenotypic and genotypic characterization. Strain H16 accumulated polyhydroxybutyrate in the presence and absence of NaCl up to 40% of its CDW.

SIGNIFICANCE AND IMPACT OF THE STUDY

This strain would be better suited for production of PHA at industrial level due to its tolerance to high concentration of NaCl.

Quenching the thirst in dialysis patients

In a double-blind cross-over trial, 22 stable end-stage renal failure patients on maintenance haemodialysis were subjected to conventional dialysis with dialysate containing 137 mEq/l sodium and constant ultrafiltration (UF) and to a different dialysis therapy, in which, by linear sodium modelling, the dialysate sodium was reduced from 137 to 128 mEq/l. A computerized UF program was used to gradually reduce the UF to a minimum towards the end of the session. Severity of thirst, interdialytic weight gain and intradialytic complications were less with low sodium dialysate. It allowed adequate UF with absolute hemodynamic stability. The reduced incidence of complication with low sodium dialysate therapy was probably because they required less UF.

Follow-up after endovascular aortic aneurysm repair can be stratified based on first postoperative imaging

Background

Lifelong postoperative surveillance is recommended following endovascular aneurysm repair (EVAR). Although the purpose is to prevent and/or identify complications early, it also results in increased cost and workload. This study was designed to examine whether it may be possible to identify patients at low risk of complications based on their first postoperative CT angiogram (CTA).

Methods

All patients undergoing EVAR in two Swedish centres between 2001 and 2012 were identified retrospectively and categorized based on the first postoperative CTA as at low risk (proximal and distal sealing zone at least 10 mm and no endoleak) or high risk (sealing zone less than 10 mm and/or presence of any endoleak) of complications.

Results

Some 326 patients (273 men) with a CTA performed less than 1 year after EVAR were included (low risk 212, 65·0 per cent; high risk 114, 35·0 per cent). There was no difference between the groups in terms of sex, age, co-morbidities, abdominal aortic aneurysm (AAA) diameter, preoperative AAA neck anatomy, stent-graft type or duration of follow-up (mean(s.d.) 4·8(3·2) years). Five-year freedom from AAA-related adverse events was 97·1 and 47·7 per cent in the low- and high-risk groups respectively (P &lt; 0·001). The corresponding freedom from AAA-related reintervention was 96·2 and 54·1 per cent (P &lt; 0·001). The method had a sensitivity of 88·3 per cent, specificity of 77·0 per cent and negative predictive value of 96·6 per cent to detect AAA-related adverse events. The number of surveillance imaging per AAA-related adverse event was 168 versus 11 for the low-risk versus high-risk group.

Conclusion

Two-thirds of patients undergoing EVAR have an adequate seal and no endoleak on the first postoperative CTA, and a very low risk of AAA-related events up to 5 years. Less vigilant follow-up after EVAR may be considered for these patients.

Magliant melanoma of the oral cavity: report of 14 cases from a regional cancer centre

Fourteen patients with oral mucosal malignant melanomas seen at a regional cancer centre over a 10-year period were analysed. All the patients presented with symptoms of short duration, with extensive local disease at initial evaluation in 11 patients. The palate was the commonest site involved. Ten patients had regional nodal disease and of these four also had distant metastases to the liver and/or the lung. Coincidental melanosis was identified clinically in three patients and histologically confirmed in two patients. Only four patients underwent radical surgery. Of the five patients who received DTIC-based chemotherapy, only one achieved a complete response. No significant correlation between stage of the disease at presentation, histological features or type of treatment and survival could be seen as the number of cases is small.

Immunoglobulins in tears of normal Indian people

Immunoglobulin concentrations in tears from 50 healthy Indians aged from 14 to 50 years were measured by a standard immunodiffusion method. The levels of IgA were substantial; those of IgG were very low; and IgD and IgM were not present. The mean IgA level was 24-6 mg/100 ml.

N-unsubstituted glucosamine in heparan sulfate of recycling glypican-1 from suramin-treated and nitrite-deprived endothelial cells. mapping of nitric oxide/nitrite-susceptible glucosamine residues to clustered sites near the core protein

We have analyzed the content of N-unsubstituted glucosamine in heparan sulfate from glypican-1 synthesized by endothelial cells during inhibition of (a) intracellular progression by brefeldin A, (b) heparan sulfate degradation by suramin, and/or (c) endogenous nitrite formation. Glypican-1 from brefeldin A-treated cells carried heparan sulfate chains that were extensively degraded by nitrous acid at pH 3.9, indicating the presence of glucosamines with free amino groups. Chains with such residues were rare in glypican-1 isolated from unperturbed cells and from cells treated with suramin and, surprisingly, when nitrite-deprived. However, when nitrite-deprived cells were simultaneously treated with suramin, such glucosamine residues were more prevalent. To locate these residues, chains were first cleaved at linkages to sulfated l-iduronic acid by heparin lyase and released fragments were separated from core protein carrying heparan sulfate stubs. These stubs were then cleaved off at sites linking N-substituted glucosamines to d-glucuronic acid. These fragments were extensively degraded by nitrous acid at pH 3.9. When purified proteoglycan isolated from brefeldin A-treated cells was incubated with intact cells, endoheparanase-catalyzed degradation generated a core protein with heparan sulfate stubs that were similarly sensitive to nitrous acid. We conclude that there is a concentration of N-unsubstituted glucosamines to the reducing side of the endoheparanase cleavage site in the transition region between unmodified and modified chain segments near the linkage region to the protein. Both sites as well as the heparin lyase-sensitive sites seem to be in close proximity to one another.