Audiometric abnormalities in children with Gaucher disease type 3

Exogenous enzyme replacement therapy achieves satisfactory biomedical correction in Gaucher type 1 disease and may halt or reverse neurological progression in type 3, while it does not appear to influence the outcome in type 2. In view of the therapeutic possibilities, early detection and monitoring of type 3 Gaucher disease, as well as evaluation of the effectiveness of enzyme therapy on neuronopathic involvement is necessary. The objective of this study was to evaluate the extent of brainstem disease in children with proven Gaucher type 3, by means of an audiological test battery. We studied 9 patients with Gaucher type 3 disease. The tests included baseline audiometric tests, as well as auditory brainstem evoked responses (ABR), acoustic reflexes and medial olivo-cochlear suppression by contralateral noise tests, that involve overlapping but not identical efferent and afferent pathways and brainstem structures. We found a constellation of abnormalities including bilaterally raised acoustic reflexes, poor medial olivo-cochlear suppression, and very poor brainstem evoked potentials. These abnormalities could be due to a single lesion in the dorsomedial brainstem, or to multiple lesions, and further study is needed to clarify this issue. Combined audiological tests may provide information on the severity of the neurological involvement and should therefore be part of a standard assessment for the diagnosis as well as for long term neurological monitoring of Gaucher type 3 patients.

Ten isoenzymes of xyloglucan endotransglycosylase from plant cell walls select and cleave the donor substrate stochastically

To map the preferred cleavage sites of xyloglucan endotransglycosylases (XETs; EC 2.4.1.207) along the donor substrate chain, we incubated the enzymes with tamarind (Tamarindus indica) xyloglucan (donor substrate; approximately 205 kDa; 21 microM) plus the nonasaccharide [(3)H]XLLGol (Gal(2).Xyl(3).Glc(3). [(3)H]glucitol; acceptor substrate; 0.6 microM). After short incubation times, to minimize multiple cleavages, the size of the (3)H-labelled transglycosylation products (determined by gel-permeation chromatography) indicated the positions of the cleavage sites relative to the non-reducing terminus of the donor. There was very little difference between the size profiles of the products formed by any of ten XETs tested [one native XET purified from cauliflower (Brassica oleracea) florets, four native XET isoenzymes purified from etiolated mung-bean (Phaseolus aureus) shoots, native XETs purified from lentil (Lens culinaris) and nasturtium (Tropaeolum majus) seeds, and three insect-cell-produced thale-cress (Arabidopsis thaliana) XETs (EXGT, TCH4 and MERI-5)]. All such product profiles showed a good fit to a model in which the enzyme chooses its donor substrate independently of size and attacks it, once only, at a randomly selected cleavage site. The results therefore do not support the hypothesis that different XET isoenzymes are adapted to produce longer or shorter products such as might favour either the efficient integration of new xyloglucan into the cell wall or the re-structuring of old xyloglucan within an expanding wall.

Osteolysis in a cementless, second generation metal-on-metal hip replacement

A 65-year-old man with osteoarthritis of the hip underwent a cementless total hip replacement with a modern generation, metal-on-metal bearing. Two years later the patient presented with localized osteolysis at the tip of the femoral stem. At the time of revision, the stem was found to be well-fixed. Extensive analyses of the bearing surfaces and periprosthetic tissues were done. There was minimal bearing surface wear and only small numbers of inflammatory cells, such as macrophages, in the tissues, and it was concluded that this was not a typical case of particle-induced osteolysis. All cultures and laboratory studies were negative for infection. This case report supports the multifactorial nature of osteolysis, which includes the osteolytic potential of joint fluid access to and fluid pressures within, the effective joint space.

Duration of symptoms and outcome of hemiresurfacing for hip osteonecrosis

Thirty-seven hips with Ficat Stage II, III, or early IV osteonecrosis were treated with hemiresurfacing. The purpose of this study is to analyze specifically the clinical and radiographic results of patients who had hemiresurfacing to refine the indications for the procedure and identify factors substantially affecting clinical outcome and survivorship. At an average followup of 6.5 years, the average University of California Los Angeles hip scores for pain, walking, function, and activity improved significantly from 4.3, 6.0, 5.3, and 4.2 to 8.0, 8.8, 7.9, and 5.8. The overall survivorship was 79%, 59%, and 45% at 5, 10, and 15 years. Eleven hips have been converted: 10 hips for acetabular cartilage wear and one hip for femoral loosening. The average time to conversion was 7.5 years. A longer duration of symptoms before surgery (16.6 months versus 12.1 months) was associated with a worse acetabular cartilage grading and suggested a relationship with a shorter time to conversion, although the difference was not statistically significant at the 5% level. Survivorship is better when preoperative symptoms are present for 1 year or less, possibly because the articular cartilage is healthier. When necessary, conversion to total hip replacement can be done without adverse results.

Estimating the cost of sea lice to salmon aquaculture in eastern Canada

Parasitic sea lice are serious problems in aquaculture. The true cost of these parasites is unknown. We demonstrate the economic burden imposed by sea lice, so that researchers, aquatic specialists, and policy makers can approximate the economic cost of this problem and work towards developing alternative control methods.

Effect of sterilization method and other modifications on the wear resistance of acetabular cups made of ultra-high molecular weight polyethylene. A hip-simulator study

BACKGROUND

Wear of ultra-high molecular weight polyethylene acetabular cups in hip prostheses produces billions of submicrometer wear particles annually that can cause osteolysis and loosening of the components. Thus, substantial improvement of the wear resistance of ultra-high molecular weight polyethylene could extend the clinical life span of total hip prostheses. It has become apparent that the conditions under which ultra-high molecular weight polyethylene cups have been sterilized can markedly affect their long-term wear properties, and new sterilization methods and other modifications have been developed to minimize the negative effects.

METHODS

In the present study, a hip-joint simulator was used to assess whether it is preferable to sterilize ultra-high molecular weight polyethylene cups without gamma irradiation, to avoid radiation-induced oxidative degradation, or to sterilize with gamma irradiation while the cups are packaged in a suitable low-oxygen atmosphere to minimize oxidation while retaining the increased wear resistance conferred by the radiation-induced cross-linking. Ion-implanted cups and cups made of a highly crystalline polyethylene (Hylamer) also were investigated. Cups made of each material were subjected to wear-testing prior to and after artificial thermal aging to accelerate oxidative degradation.

RESULTS

The results of the present study demonstrated that the cross-linking induced by gamma irradiation improves the wear resistance of ultra-high molecular weight polyethylene, while oxidation reduces it. Without thermal aging, the two types of cups that were sterilized with gamma irradiation while in low-oxygen packaging exhibited about a 50 percent lower rate of wear than did either the nonsterilized cups or the nonirradiated cups sterilized with gas plasma. There was a comparable advantage in the rate of wear after fourteen days of thermal aging. However, after thirty days of aging, the cups sterilized with gamma irradiation in low-oxygen packaging wore several times faster than did the nonirradiated cups. Ion-implanting improved the wear resistance without thermal aging, but after extensive thermal aging the oxidation and wear were greater than those of the controls. Hylamer cups (that is, those that were sterilized with gas plasma) exhibited wear properties very close to those of the nonsterilized ultra-high molecular weight polyethylene cups (the controls) with or without aging.

CONCLUSIONS

Sterilizing an ultra-high molecular weight polyethylene acetabular cup without radiation (for example, with ethylene oxide or gas plasma) avoids immediate and long-term oxidative degradation of the implant but does not improve the inherent wear resistance of the polyethylene. Sterilizing with use of gamma irradiation with the implant packaged in a low-oxygen atmosphere avoids immediate oxidation and cross-links the polyethylene, thereby increasing its wear resistance, but long-term oxidation of the residual free radicals may markedly reduce the wear resistance. Ideally, cross-linking with gamma irradiation to reduce wear should be done in a manner that avoids both immediate and long-term oxidation.

Tracing cranial nerve pathways (glossopharyngeal, vagus, and hypoglossal) in SIDS and control infants: a DiI study

It has been proposed that Sudden Infant Death Syndrome (SIDS) might occur as a consequence of a developmental deficit associated with the cardiorespiratory and arousal control centers located within the brainstem. In this study 1.1' dioctadecyl-3,3,3',3-tetramethylindocarbocyanine perchlorate (DiI) was used to investigate the trajectories of the glossopharyngeal and vagus nerves which carry essential afferent and efferent fiber tracts associated with cardiac and respiratory control and of the hypoglossal nerve which innervates the tongue, in SIDS (n = 14) and control (n = 7) infants. The postnatal development of the trajectories of these nerves was examined in non-SIDS brains and comparisons were then made with age-matched SIDS brains. The mean profile area of hypoglossal and dorsal motor neurons were also assessed. In controls, no major alterations were observed in the trajectories of axon bundles with increasing age (7 wk to 2 yr) in each of the nerves investigated although axon bundles appeared to increase in thickness with age. In SIDS cases (2 wk to 44 wk), the trajectories of the cranial nerves were not different from those seen in age-matched control cases. The mean profile area of hypoglossal and dorsal motor neurons was not significantly different between control and SIDS infants. We conclude that the DiI tracing technique can be used successfully to trace the pathways of cranial nerves in human infant fixed-tissue. Furthermore, if functional differences exist between SIDS and non-SIDS brains in the control of respiration, circulation, or arousal they do not appear to be related to markedly reduced or aberrant projections of the glossopharyngeal, vagus, or hypoglossal nerves.

Effect of hemoglobin levels in hemodialysis patients with asymptomatic cardiomyopathy

BACKGROUND

Hemoglobin levels below 10 g/dL lead to left ventricular (LV) hypertrophy, LV dilation, a lower quality of life, higher cardiac morbidity, and a higher mortality rate in end-stage renal disease. The benefits and risks of normalizing hemoglobin levels in hemodialysis patients without symptomatic cardiac disease are unknown.

METHODS

One hundred forty-six hemodialysis patients with either concentric LV hypertrophy or LV dilation were randomly assigned to receive doses of epoetin alpha designed to achieve hemoglobin levels of 10 or 13.5 g/dL. The study duration was 48 weeks. The primary outcomes were the change in LV mass index in those with concentric LV hypertrophy and the change in cavity volume index in those with LV dilation.

RESULTS

In patients with concentric LV hypertrophy, the changes in LV mass index were similar in the normal and low target hemoglobin groups. The changes in cavity volume index were similar in both targets in the LV dilation group. Treatment-received analysis of the concentric LV hypertrophy group showed no correlation between the change in mass index and a correlation between the change in LV volume index and mean hemoglobin level achieved (8 mL/m2 per 1 g/dL hemoglobin decrement, P = 0.009). Mean hemoglobin levels and the changes in LV mass and cavity volume index were not correlated in patients with LV dilation. Normalization of hemoglobin led to improvements in fatigue (P = 0.009), depression (P = 0.02), and relationships (P = 0.004).

CONCLUSIONS

Normalization of hemoglobin does not lead to regression of established concentric LV hypertrophy or LV dilation. It may, however, prevent the development of LV dilation, and it leads to improved quality of life.

Tibioperoneal arterial lesions and critical foot ischaemia: successful management by the use of short vein grafts and percutaneous transluminal angioplasty

BACKGROUND

In a substantial number of mainly diabetic patients isolated crural arterial lesions are found to be the underlying cause for severe ischaemic foot lesions. Without revascularisation, patients with this specific occlusion pattern will inevitably face major amputation. To attain limb salvage in this setting, since the early eighties short vein grafts were used to bypass the occluded infrapopliteal arteries. More recently, percutaneous transluminal angioplasty (PTA) was also attempted to avoid limb loss in selected patients.

PATIENTS AND METHODS

Since May 1986 in 125 patients 130 autologous bypass grafts from the BK-popliteal artery or the proximal tibioperoneal arteries to malleolar vessels were performed in the presence of extended crural arterial occlusions and critical foot ischaemia (rest pain 3, tissue loss 127). In another series in 89 limbs (rest pain 5, tissue loss 84) of 84 patients PTA was done to treat 168 focal stenoses of > 50% diameter reduction and 11 short occlusions in a total of 135 crural arteries.

RESULTS

Using life-table analysis, primary and secondary cumulative patency rates for short vein grafts with distal graft origin were 90% and 98% at 30 days, 76% and 83% at one year and 46% and 49% at seven years, respectively. The corresponding limb salvage rates amounted to 95%, 80% and 63%. Initial complete or partial technical success after PTA of crural arteries could be obtained in 93%: The limb salvage rates achieved were 95% at 30 days, 82% at one year and 63% at six years.

CONCLUSION

Our results suggest that--depending on the extent of lesions--both short vein grafts as well as PTA are successful complementary treatment modalities to avoid limb loss in predominantly diabetic patients with infrapopliteal artery disease and critical ischaemia.

Shapes and dimensional characteristics of polyethylene wear particles generated in vivo by total knee replacements compared to total hip replacements

Periprosthetic tissue was obtained at revision surgery from 10 posterior cruciate retaining total knee replacement cases (five different manufacturers). The tissues were hydrolyzed and polyethylene particles were isolated from each case. Individual particles were analyzed by scanning electron microscopy combined with computerized image analysis. For comparison, periprosthetic tissues from 10 total hip replacement cases (six different manufacturers) were processed and analyzed simultaneously with identical methods. The morphologies of the isolated polyethylene particles from total knee specimens were distinctly different. There was more variety of size, shape, and texture in the total knee particles. Submicron granules were less prevalent than in hip specimens. Larger flake-shaped particles, some measuring several microns in length and width, were commonly seen in knee specimens but not hip specimens. The overall average area of particles from the total knees (1.2 microns2) was twice that of total hips (0.61 micron2) (p = 0.049). The average perimeter (p = 0.026) and length (p = 0.026) of total knee particles was also greater than the total hip particles. The proportion of the smallest polyethylene particles (those averaging 0.2 micron2) in the total knee specimens was significantly less than that in total hip specimens (p < 0.0001). Although the large flake-shaped particles were visually striking, it is important to note that the majority of the wear particles from the total knee cases were also submicron. These differences in wear particle morphology and size are due to differences in the wear mechanisms of total knees and total hips. Size is only one parameter in wear particle bioreactivity. Other factors include particle shape, surface area, and possibly size/shape variability, as well as surface chemistry and particle concentration. Polyethylene wear particles are not unidimensional; they have complex and variable shapes. The combination of morphologic description and quantitative image analysis used in this study defines several differences in polyethylene wear particles from different sources.

Comparative hospitalization of hemodialysis and peritoneal dialysis patients in Canada

BACKGROUND

Most comparisons of hemodialysis (HD) and peritoneal dialysis (PD) have used mortality as an outcome. Relatively few studies have directly compared the hospitalization rates, an outcome of perhaps equal importance, of patients using these different dialysis modalities.

METHODS

Eight hundred twenty-two consecutive patients at 11 Canadian institutions with irreversible renal failure had an extensive assessment of comorbid illness and initial mode of dialysis collected prospectively immediately prior to starting dialysis therapy. The cohort was assembled between March 1993 and November 1994. The mean follow-up was 24 months. Admission data were used to compare hospitalization rates in HD and PD.

RESULTS

Thirty-four percent of patients at baseline and 50% at three months used PD. Twenty-five percent of HD and 32% of PD patients switched dialysis modality at least once after their first treatment (P = NS). Nine percent of HD patients and 30% of PD patients switched modality after three months (P < 0. 001). Total comorbidity was higher in HD patients at baseline (P < 0. 001) and at three months (P = 0.001). The overall hospitalization rate was 40.2 days per 1000 patient days after baseline and 38.0 days per 1000 patient days after three months. When an adjustment was made for baseline comorbid conditions, patients on PD had a lower rate of hospitalization in intention-to-treat analysis according to the type of dialysis in use at baseline (RR 0.85, 95% CI, 0.82 to 0.87, P < 0.001), but a higher rate according to the type of dialysis in use three months after study entry (RR 1.31, 95% CI, 1.27 to 1.34, P < 0.001). In analyses based on the amount of time actually spent on each treatment modality, PD was associated with a higher rate of hospitalization when analyzed according to the type of dialysis in use at baseline (RR 1.10, 95% CI, 1.07 to 1.13, P < 0.001) and according to the type of dialysis in use three months after study entry (RR 1.26, 95% CI, 1.23 to 1.30, P < 0.001).

CONCLUSIONS

Conclusions regarding comparative hospitalization rates are heavily dependent on the analytic starting point and on whether intention-to-treat or treatment-received analyses are used. When early treatment switches are accounted for, HD is associated with a lower rate of hospitalization than PD, but the effect is modest.

Extensive metallosis and necrosis in failed prostheses with cemented titanium-alloy stems and ceramic heads

We describe three prostheses with cemented titanium-alloy stems and Al2O3 ceramic femoral heads which had to be revised after a mean period of implantation of 78 months. In each case, the neck of the prosthesis had been so severely worn that the profile was elliptical rather than circular. There was severe metallosis of the periprosthetic tissues. Metal particles isolated from the tissues were approximately one nanometre in size and the ratios of titanium, aluminium and vanadium in the particles were the same as in the original alloy. Histologically, the high concentration of metal particles masked the presence of high-density polyethylene (HDP) debris, but again particles about one nanometre in size were isolated from the tissues. The severe necrobiosis and necrosis noted were consistent with other reports of the presence of extensive wear particles in periprosthetic tissues. Wear is presumed to have occurred as a result of mismatch between the shape or size of the taper cone and the femoral head, or to changes in the geometry of loading due to migration of the cup. To facilitate early intervention, patients with this design of prosthesis should be monitored radiologically.

Postoperative nausea and vomiting in women following breast surgery: an audit

A prospective observational study of 101 women having breast surgery under general anaesthesia was performed to assess the extent of postoperative nausea and vomiting in this group of women. The overall rate of postoperative nausea and vomiting was high, 56% and 41%, respectively, and was significantly associated with length of surgical procedure and morphine use. Techniques to reduce morphine requirement should be evaluated to try and reduce this cause of morbidity.

Toxicity of non-abeta component of Alzheimer's disease amyloid, and N-terminal fragments thereof, correlates to formation of beta-sheet structure and fibrils

The non-Abeta component of Alzheimer's disease amyloid (NAC) and its precursor alpha-synuclein have been linked to amyloidogenesis in Alzheimer's disease (AD), Parkinson's disease (PD) and dementia with Lewy bodies (DLB). Previously we have shown that NAC forms beta-sheet structures and fibrils [El-Agnaf, O.M.A., Bodles, A.M., Guthrie, D.J.S., Harriott, P. & Irvine, G.B. (1998) Eur. J. Biochem. 258, 157-163]. As a measure of their neurotoxic potential we have examined the ability of fresh and aged NAC and fragments thereof to inhibit the reduction of the redox dye 3-(4, 5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide by rat pheochromocytoma PC12 cells. Micromolar concentrations of NAC and fragments thereof display varying degrees of toxicity. On immediate dissolution and after an incubation period for 3 days at 37 degrees C the full-length peptide and fragments NAC(3-18) and NAC(1-18) scrambled sequence [NAC(1-18 s)] were toxic, whereas fragments NAC(1-13) and NAC(6-14) were not. CD indicates that NAC(3-18) and NAC(1-18 s) exhibit beta-sheet secondary structure in aqueous solution, whereas NAC(1-13) and NAC(6-14) do not. NAC(3-18) aggregates, as indicated by concentration of peptide remaining in solution after 3 days measured by an HPLC assay, and forms fibrils, as determined by electron microscopy. However, although some fibrils were detected for NAC(1-18 s) it does not come out of solution to a significant degree. Fragments NAC(1-13) and NAC(6-14) form few fibrils and remain in solution. These findings indicate that the ability of the central region of NAC to form beta-sheet secondary structures is important for determining the toxicity of the peptide. This contrasts with what has been reported previously for most Abeta peptides as their toxicity appears to require the peptide to have formed fibrillary aggregates as well as displaying beta-sheet. These results suggest that an intermediate, which exhibits beta-sheet structure, may be responsible for the toxic properties of NAC and provides further evidence for the role of NAC in the pathogenesis of AD, PD and DLB.

Comparative mortality of hemodialysis and peritoneal dialysis in Canada

BACKGROUND

Comparisons of mortality rates in patients on hemodialysis versus those on peritoneal dialysis have been inconsistent. We hypothesized that comorbidity has an important effect on differential survival in these two groups of patients.

METHODS

Eight hundred twenty-two consecutive patients at 11 Canadian institutions with irreversible renal failure had an extensive assessment of comorbid illness collected prospectively, immediately prior to starting dialysis therapy. The cohort was assembled between March 1993 and November 1994; vital status was ascertained as of January 1, 1998.

RESULTS

The mean follow-up was 24 months. Thirty-four percent of patients at baseline, 50% at three months, and 51% at six months used peritoneal dialysis. Values for a previously validated comorbidity score were higher for patients on hemodialysis at baseline (4.0 vs. 3.1, P < 0.001), three months (3.7 vs. 3.2, P = 0.001), and six months (3.6 vs. 3.2, P = 0.005). The overall mortality was 41%. The unadjusted peritoneal dialysis/hemodialysis mortality hazard ratios were 0.65 (95% CI, 0. 51 to 0.83, P = 0.0005), 0.84 (95% CI, 0.66 to 1.06, P = NS), and 0. 83 (95% CI, 0.64 to 1.08, P = NS) based on the modality of dialysis in use at baseline, three months, and six months, respectively. When adjusted for age, sex, diabetes, cardiac failure, myocardial infarction, peripheral vascular disease, malignancy, and acuity of renal failure, the corresponding hazard ratios were 0.79 (95% CI, 0. 62 to 1.01, P = NS), 1.00 (95% CI, 0.78 to 1.28, P = NS), and 0.95 (95% CI, 0.73 to 1.24, P = NS). Adjustment for a previously validated comorbidity score resulted in hazard ratios of 0.74 (95% CI, 0.58 to 0.94, P = 0.01), 0.94 (95% CI, 0.74 to 1.19, P = NS), and 0.88 (95% CI, 0.68 to 1.13, P = NS) at baseline, three months, and six months. There was no survival advantage for either modality in any of the major subgroups defined by age, sex, or diabetic status.

CONCLUSIONS

The apparent survival advantage of peritoneal dialysis in Canada is due to lower comorbidity and a lower burden of acute onset end-stage renal disease at the inception of dialysis therapy. Hemodialysis and peritoneal dialysis, as practiced in Canada in the 1990s, are associated with similar overall survival rates.

Thyroid pathology associated with primary hyperparathyroidism

BACKGROUND

Thyroid carcinoma and benign thyroid disease associated with primary hyperparathyroidism (PHPT) have been well described. With the developing trend toward minimally invasive parathyroidectomy without intra-operative thyroid gland palpation, thyroid pathology may be missed. The authors consider it timely to revisit the issue of thyroid pathology found at neck exploration for PHPT.

METHODS

A retrospective review of all cases of neck exploration for PHPT between 1993 and 1998 at Liverpool Hospital was undertaken.

RESULTS

There were 65 patients in the study group (44 women, 21 men; mean age: 59 years). The most common indication for surgery was asymptomatic hypercalcaemia. The mean pre-operative calcium level was 2.9 mmol/L and the mean parathyroid hormone (PTH) level was 17 pmol/L. There were 26 cases (40%) of coexistent thyroid pathology. Ten cases (15%) were of mild multinodular change, seven cases (11%) were of severe multinodular change requiring thyroidectomy, three cases (4%) were nodules secondary to Hashimoto's thyroiditis and six cases (10%) were suspicious nodules that proved to be either adenomas (n = 3) or carcinomas (n = 3) following excision. There were four papillary carcinomas detected in the present series with a mean metastases, age, completeness of excision, invasion size (MACIS) score of 4.92.

CONCLUSION

A 25% association of significant thyroid pathology with PHPT is reported. Despite pre-operative tests there were two cases (4%) of thyroid carcinoma where the decision to resect the thyroid gland was made following intra-operative thyroid gland palpation. One of these two papillary carcinoma patients would have fulfilled criteria for minimally invasive parathyroid surgery. When evaluating results of minimally invasive parathyroid surgery one must be aware of the potential for missed thyroid pathology.

Extensive metallosis and necrosis in failed prostheses with cemented titanium-alloy stems and ceramic heads

We describe three prostheses with cemented titanium-alloy stems and Al2O3 ceramic femoral heads which had to be revised after a mean period of implantation of 78 months. In each case, the neck of the prosthesis had been so severely worn that the profile was elliptical rather than circular. There was severe metallosis of the periprosthetic tissues. Metal particles isolated from the tissues were approximately one nanometre in size and the ratios of titanium, aluminium and vanadium in the particles were the same as in the original alloy. Histologically, the high concentration of metal particles masked the presence of high-density polyethylene (HDP) debris, but again particles about one nanometre in size were isolated from the tissues. The severe necrobiosis and necrosis noted were consistent with other reports of the presence of extensive wear particles in periprosthetic tissues. Wear is presumed to have occurred as a result of mismatch between the shape or size of the taper cone and the femoral head, or to changes in the geometry of loading due to migration of the cup. To facilitate early intervention, patients with this design of prosthesis should be monitored radiologically.

Biosynthesis of heparin/heparan sulfate: kinetic studies of the glucuronyl C5-epimerase with N-sulfated derivatives of the Escherichia coli K5 capsular polysaccharide as substrates

The D-glucuronyl C5-epimerase involved in the biosynthesis of heparin and heparan sulfate was investigated with focus on its substrate specificity, its kinetic properties, and a comparison of epimerase preparations from the Furth mastocytoma and bovine liver, which synthesize heparin and heparan sulfate, respectively. New substrates for the epimerase were prepared from the capsular polysaccharide of Escherichia coli K5, which had been labeled at C5 of its D-glucuronic and N-acetyl-D-glucosamine moieties by growing the bacteria in the presence of D-[5-(3)H]glucose. Following complete or partial ( approximately 50%) N-deacetylation of the polysaccharide by hydrazinolysis, the free amino groups were sulfated by treatment with trimethylamine.SO(3)complex, which yielded products that were recognized as substrates by the epimerase and released tritium from C5 of the D-glucuronyl residues upon incubation with the enzyme. Comparison of the kinetic properties of the two substrates showed that the fully N-sulfated derivative was the best substrate in terms of its K(m)value, which was significantly lower than that of its partially N-acetylated counterpart. The V(max)values for the E.coli polysaccharide derivatives were essentially the same but were both lower than that of the O-desulfated [(3)H]heparin used in our previous studies. Surprisingly, the apparent K(m)values for all three substrates increased with increasing enzyme concentration. The reason for this phenomenon is not entirely clear at present. Partially purified C5-epimerase preparations from the Furth mastocytoma and bovine liver, respectively, behaved similarly in terms of their reactivity towards the various substrates, but the variation in apparent K(m)values with enzyme concentration precluded a detailed comparison of their kinetic properties.