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Biomedical subjects

Y S Chan

Publications and source records attributed to Y S Chan.

At least 55 records · Page 3Linked to original sources
PubMed2000

Vascularized island pedicle iliac bone grafting for avascular necrosis of the femoral head.

BACKGROUND: Nontraumatic avascular necrosis of the femoral head is a common disorder causing disability of the hip joint. The methods for optimally treating this disease in active young patients are still controversial. In this study we investigated the surgical outcome of vascularized pedicle iliac bone grafting for treating nontraumatic avascular necrosis of the femoral head. METHODS: Between 1994 and 1999, we treated 100 cases of avascular necrosis of the femoral head with vascularized pedicle iliac bone grafting. Thirty-nine hips in 33 patients were followed-up longer than 24 months. These patients included 30 men and 3 women, with an average age of 40 years. Steinberg's classification and Ohzono's types were used to categorize the diseased hips. The clinical results were evaluated using Charnley's modification of Merle d'Aubigne and Postel's numeric classification. RESULTS: Of the 33 patients, 82% were satisfied with their decision to have vascularized pedicle iliac bone grafting for avascular necrosis of the femoral head. No serious complications arose during this study. The average operation time for vascularized pedicle iliac bone grafting was 3.5 hours for one team. The rate of conversion to replacement arthroplasty was 10.3% (4 of 39 patients). CONCLUSION: Vascularized pedicle iliac bone grafting is a useful alternative treatment option for patients with avascular necrosis of the femoral head.

Adult↗
PubMed1999

The molecular basis for the B(A) allele: an amino acid alteration in the human histoblood group B alpha-(1,3)-galactosyltransferase increases its intrinsic alpha-(1,3)-N-acetylgalactosaminyltransferase activity.

The formation of the subgroup B(A) phenotype is thought to be due to an overlapping specificity of the human blood group A and B transferases. A new molecular basis for the B(A) allele, resulting from the C(700) to G substitution which predicts the alteration of Pro(234) to Ala, just ahead of the second of the four amino acid residues which differentiates the specificities of the A and B transferases, is reported here. Compared to normal group B sera, a relatively lower B-transferase activity was demonstrated in the B(A) serum, which correlated well with the observation of a smaller amount of B antigen on the B(A) red cells. Also a much higher A-transferase activity was demonstrated in the B(A) serum in contrast to the minute amount of A-transferase activity found in normal group B sera. The formation of the B(A) phenotype in this report is most likely due to the shifting of the specificity of the B transferase rather than an enhanced B-transferase activity which was previously presumed to be responsible for the formation of this phenotype. The Pro(234) to Ala alteration is suggested to be responsible for the shifting of the specificity with a subsequent increase in A- but a decrease in B-transferase activity. This new B(A) allele shows that not only the four critical residues but also the neighboring areas may influence the specificity of the A and B transferases.

ABO Blood-Group System↗
PubMed1999

Lipoprotein lipase mutations and Alzheimer's disease.

Lipoprotein lipase (LPL) helps transfer lipids from lipoprotein particles to cells. In the brain, LPL is present in Alzheimer's disease (AD) amyloid plaques. LPL binds apolipoprotein E (ApoE) lipoprotein particles and low-density lipoprotein receptor-related protein (LRP), an ApoE receptor. Since polymorphisms in both ApoE and LRP influence AD risk, we sought to determine whether LPL mutations also affect AD risk. In a case-control study, the frequencies of two of the most common known LPL mutations were measured in European-Americans either clinically diagnosed or pathologically confirmed as AD or normal control (N) subjects. In clinically diagnosed subjects, the Ser447Ter mutation comprised 9.8% (62/630) of alleles in N and 3.8% (9/238) in AD, a significant difference (P = 0.0057), while the Asn291Ser mutation comprised 1.1% (5/460) of alleles in N and 5.1% (8/158) in AD, also a significant difference (P = 0.0073), though in pathologically confirmed subjects the allele frequencies for AD did not significantly differ from N for either mutation. In clinically diagnosed subjects, LPL mutations were associated with altered AD risk, suggesting a potential role for LPL in the causation of AD. Further studies in different populations should help clarify the questions raised by these results.

Aged↗
PubMed1999

Codisposal of municipal refuse, sewage sludge and marine dredgings for methane production.

As marine disposal of sewage sludge and dredged sediments may impose serious adverse effects to marine ecosystems, landfilling seems to be the most feasible method for the final disposal of these wastes. A batch experiment was conducted to study waste degradation and gas production after sewage sludge and marine dredgings were mixed with municipal refuse at 13 different ratios for 36 days. The addition of sludge and dredgings to municipal refuse enhanced gas production, compared with the degradation of refuse or sludge alone. A proper mixing ratio of wastes can also shorten the time to reach the final phase of anaerobiosis. The highest gas production was obtained from the ratio of 75-20-5 (refuse-sludge-dredgings) (wet weight basis). Its average daily gas production rate was 1.42 l kg(-1) waste mixture; methane content was 68.3%. The results indicated that codisposal of the three wastes would be beneficial for energy recovery from landfill gas.

Journal Article↗
PubMed1999

Neuronal response sensitivity to bidirectional off-vertical axis rotations: a dimension of imbalance in the bilateral vestibular nuclei of cats after unilateral labyrinthectomy.

In decerebrate cats after acute hemilabyrinthectomy, the response sensitivity of extracellularly recorded vestibular nuclear neurons on the lesioned and labyrinth-intact sides were examined quantitatively during constant velocity off-vertical axis rotations with an aim to elucidate the functional contribution of otolithic inputs to the ipsilateral and contralateral vestibular nuclei. The bidirectional response sensitivity, delta, was determined as the ratio of the gain during clockwise to that during counterclockwise rotations. A continuum of response sensitivity was identified: one-dimensional neurons showed symmetrically bidirectional response patterns, while two-dimensional neurons showed asymmetrically bidirectional patterns that in some cases approached unidirectional patterns with change in velocity. The proportion of two-dimensional neurons was significantly increased after acute hemilabyrinthectomy. Two-dimensional neurons that responded only to one direction of rotation in at least one of the velocities tested were described as unidirectional neurons. This unidirectional response pattern was observed in one-third of the entire neuronal population studied, but not in cats with both labyrinths intact, thus suggesting that such prominent broadly tuned responses are normally masked by converging otolithic inputs from the contralateral side. These neurons were found in higher proportion on the lesioned side than on the labyrinth-intact side. Among the 70% of unidirectional neurons that exhibited bidirectional response at some velocities and unidirectional response at others, prominent shifts in delta values (i.e. between 0/infinity and finite values) with velocity can be computed for each neuron. The shifts in delta values correlated with large shifts in the response dynamics and spatial orientation as the response pattern changed with velocity. The response orientations of the unidirectional neurons pointed in all directions on the horizontal plane. When all the two-dimensional neurons (i.e. both the unidirectionally and bidirectionally responsive ones) were pooled, imbalances in the distribution of the response orientations and in response gain were found between the ipsilateral-side-down/head-down half-circle and the contralateral-side-down/head-up half-circle on the labyrinth-intact side, but not on the lesioned side. These results, derived from spatiotemporal processing of gravitational signals, reveal a novel dimension of imbalance between neuronal populations in the two vestibular nuclear complexes after acute lesion of one labyrinth. This feature would provide, on the one hand, deranged cues of spatial orientation and direction during slow head excursions and, on the other, a framework for the dynamic behavioral deficits associated with hemilabyrinthectomy.

Animals↗
PubMed1999

Inducible isopentenyl transferase as a high-efficiency marker for plant transformation.

Overexpression of the isopentenyltransferase gene (ipt) from the Ti-plasmid of Agrobacterium tumefaciens increases cytokinin levels, leading to generation of shoots from transformed plant cells. When combined with a dexamethasone-inducible system for controlling expression, ipt expression can be used to select for transgenic regenerants without using an antibiotic-resistance marker. The combined system allows efficient cointroduction of multiple genes (in addition to ipt) and produces transgenic plants without morphological or developmental defects.

Agrobacterium tumefaciens↗
PubMed1999

Heparan sulphates upregulate regeneration of transected sciatic nerves of adult guinea-pigs.

The increased content of soluble glycosaminoglycan-containing forms in sciatic nerves during recovery from crush injury [Shum & Chau (1996) J. Neurosci. Res., 46, 465] suggests that the glycosaminoglycans modulate the environment for post-traumatic tissue remodelling and axonal regrowth. To test this, defined amounts of soluble heparan sulphates from bovine kidney or guinea-pig nerve were introduced into the regenerating environment via silicone conduits that bridged 8-mm gaps of transected sciatic nerves of adult guinea-pigs. Controls were bridged using the phosphate-buffered saline (PBS) vehicle or a chondroition sulphate preparation from whale cartilage. After timed periods of recovery, the animals were assessed for electromyographic signals at the target gastrocnemius muscle to determine the conduction velocity across the bridged nerve. Sections of the bridge were also histologically examined for nerve fibres. Transected sciatic nerves bridged with heparan sulphates or chondroitin sulphate showed earlier stimulated myelination of axons (week 5-6) than PBS-bridged nerves (week 9). Initial electromyographic indication of reconnection with the target was at week 9 post-transection. In the course of 20 weeks, transected sections of the bridge indicated similar numbers of unmyelinated axons irrespective of bridge material, but distinctly higher numbers of myelinated axons in heparan sulphate-bridged nerves than either PBS- or chondroitin sulphate-bridged nerves. At the end of the same period, heparan sulphate-bridged nerves resumed normal conduction velocities, but both PBS- and chondroitin sulphate-bridged nerves remained at 50% of that of the intact contralateral nerves. These results are the first to demonstrate that supplementation of soluble heparan sulphate to the fluid regenerative neural environment can restore functional, axonal reconnection of the severed nerve with the target muscle.

Animals↗
PubMed1999

In vitro elution of antibiotic from antibiotic-impregnated biodegradable calcium alginate wound dressing.

OBJECTIVE: The authors investigated the calcium alginate dressing as a drug-delivery system for the treatment of various surgical infections. METHODS: Cytotoxicity of the calcium alginate dressing to fibroblasts and HeLa cells was evaluated by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide (MITT) colorimetric assay. The calcium alginate dressing was mixed with vancomycin, and lyophilized or not lyophilized to form two types of antibiotic dressings. The antibiotic dressings were placed in 2 mL of phosphate buffered saline (PBS) or in PBS containing 0.01% calcium ions, and incubated at 37 degrees C. The PBS was changed daily, and the removed solutions were stored at -70 degrees C until the antibiotic concentration in each sample was determined by high performance liquid chromatography assay. RESULTS: The results suggested that the antibiotic dressings present no obvious toxic risk to their use as a drug-delivery system. The concentration of vancomycin in each sample was well above the breakpoint sensitivity concentration (the antibiotic concentration at the transition point between bacterial kill. ing and resistance to the antibiotic) for more than 14 days. The release was most marked during the first 48 hours. The concentration of calcium ions in PBS and the lyophilization of the manufacture process of antibiotic dressings prolonged the antibiotic diffusion duration. The diameter of the sample inhibition zone ranged from 10 to 11 mm, and the relative activity of vancomycin ranged from 62.88% to 92.18%. CONCLUSION: All antibiotic dressings released bactericidal concentrations of the antibiotics in vitro for the period of time needed to treat surgical infections. This study offers a convenient method to meet the specific antibiotic requirement for different patients.

Alginates↗
PubMed1998

Spontaneous activity and barosensitivity of the barosensitive neurons in the rostral ventrolateral medulla of hypertensive rats induced by transection of aortic depressor nerves.

In order to determine the role of the rostral ventrolateral medulla (RVLM) in the development of neurogenic hypertension, the aortic depressor nerves of rats were transected (tADN) to produce neurogenic hypertension. The rate and pattern of firing of the barosensitive RVLM neurons of the treated rats were studied. In neurogenic hypertensive rats, the RVLM barosensitive neurons exhibited a faster firing rate and a shorter interspike interval (ISI) than the corresponding values of the control and sham groups, indicating an enhanced spontaneous activity of these neurons in the hypertensive rats. The coefficient of variation (cv) and skewness (sk) of the ISI histogram, parameters reflecting the regularity of neuronal firing, were smaller in neurogenic hypertensive than in the control and sham-operated rats. Following tADN, the responsiveness of these neurons to blood pressure changes was attenuated, suggesting a reduced intrinsic barosensitivity of neurons and/or a reduced baroreceptor input. The increase in spontaneous activity and firing regularity of RVLM barosensitive neurons imply an enhancement in the efficacy of outflow from these neurons. The increased efficacy of the outflow from the RVLM barosensitive neurons and the resetting of the baroreflex may contribute to the genesis of neurogenic hypertension.

Animals↗
PubMed1998

Low density lipoprotein receptor related protein gene exon 3 polymorphism association with Alzheimer's disease in Chinese.

Since apolipoprotein E4 (apoE4) is the major genetic risk for late onset Alzheimer's disease (AD), proteins that interact with apoE might be involved in AD pathogenesis. Low density lipoprotein receptor related protein (LRP) is an apoE receptor in the brain. In exon 3 of the LRP gene a polymorphism was found to be underrepresented in AD compared to normal Caucasian subjects (N). We examined this polymorphism in Chinese AD and N subjects. The polymorphism frequency in N was roughly half that reported for Caucasians. Compared to N, the frequency was significantly decreased in pathologically diagnosed, but not in clinically diagnosed AD patients. Thus, the role of the LRP exon 3 polymorphism in AD has now been demonstrated in two ethnic groups, suggesting the importance of LRP in AD pathogenesis.

Aged↗
PubMed1998

No association detected between very-low-density lipoprotein receptor (VLDL-R) and late-onset Alzheimer's disease in Hong Kong Chinese.

The epsilon4 allele of apolipoprotein E (ApoE) is a risk factor in late-onset Alzheimer's disease (AD). As a receptor for ApoE, very-low-density lipoprotein receptor (VLDLR) might be involved in AD pathogenesis. A Japanese study [Okuizimi, K., et al., Nature Genet., 11 (1995) 207-209] has shown an increased 5 and decreased 8 CGG-repeat allele frequency in the 5' untranslated region of VLDLR in Japanese AD versus normal controls (N). Subsequent studies in Caucasian Americans failed to duplicate the result. We examined this polymorphism in pathologically- or clinically-diagnosed Chinese late-onset AD. Our data did not show a significant increase in the 5 CGG-repeat in AD, thus suggesting no association to VLDLR. However, our data did show that the allele frequencies for each CGG-repeat were similar in both Chinese and Japanese.

Age of Onset↗
PubMed1998

Management of small infected tibial defects with antibiotic-impregnated autogenic cancellous bone grafting.

Between January of 1991 and December of 1993, 36 patients who had tibia fractures complicated by small infected tibia defects were treated at the authors' service. The group included 30 men and 6 women whose average age was 36.5 years (range, 18-72 years). The average follow-up period was 3.7 years. By using the Cierney-Mader staging classification of chronic osteomyelitis, 26 of 36 patients (72%) were stage 4A and 10 of 36 patients (28%) were stage 4B. Ten patients required muscle transfer. All patients were treated with a two-stage protocol. In the first stage, antibiotic-impregnated polymethylmethacrylate bead chains were used to obliterate the debrided osseous defect. In the second stage, the beads were removed, and the defects were reconstructed with antibiotic-impregnated autogenic cancellous bone graft. The time between the first and second stage was 2 to 8 weeks for patients without muscle transfer and 8 to 12 weeks for the patients with muscle transfer. The bone defects ranged from 2 to 4 cm. Wound healing and bony union were achieved in all patients. Only two patients had recurrent infections. The infection arrest rate was 94.4%. Minor pin tract infection of the external skeletal fixation was seen in two patients. Two patients developed skin rashes secondary to antibiotic therapy. Radiographs at an average follow-up of 3.7 years showed good consolidation and hypertrophy of grafted bones in all patients. After 3 to 5 years of follow-up, our results suggest that the use of impregnating antibiotics have no adverse effects on autogenic cancellous bone graft incorporation and may help to eliminate infection. This treatment protocol provided rapid recovery from osteomyelitis. The use of antibiotic-impregnated autogenic bone graft seems to be an effective and safe method for the management of small infected tibial defects.

Adolescent↗
PubMed1998

Glucose-6-phosphatase gene (727G-->T) splicing mutation is prevalent in Hong Kong Chinese patients with glycogen storage disease type 1a.

Glycogen storage disease type la (GSD1a) is an autosomal recessive metabolic disorder caused by a deficiency in glucose-6-phosphatase (G6Pase). We analyzed the G6Pase genes of two unrelated Chinese families with GSD1a. DNA sequencing of all five exons and the exon-intron boundaries revealed a G T transversion at nucleotide 727 (727G-->T) in exon 5, which has previously been reported to cause abnormal splicing. In one family, the subject and her affected sister were confirmed to be homozygous for this mutation and their parents to be heterozygotes. In the other family, the proband was identified to be heterozygous for this mutation, and a novel mutation, the 341delG in exon 2, was identified. This mutation alters the reading frame and creates a stop codon TAA 15 codons downstream from the mutation, resulting in a truncated protein. Family studies revealed that the father was heterozygous for the 727G-->T mutation and that the mother was heterozygous for the 341delG mutation. This is the first time that the 727G T mutation has been found in Chinese patients or outside Japan. Since we only tested two GSD1a families and found 727G-->T in both, we believe that this mutation may also be prevalent in our local Chinese population. To investigate allele frequencies, we screened 385 Chinese healthy volunteers and found two asymptomatic carriers. Our findings suggest that the 727G-->T mutation is indeed prevalent in Hong Kong.

Base Sequence↗
PubMed1998

Mutations in the low-density lipoprotein receptor gene in Chinese familial hypercholesterolemia patients.

It has been reported that in China, patients with heterozygous familial hypercholesterolemia (FH) may go unrecognized because they do not have xanthomata or premature coronary heart disease and their LDL cholesterol levels are lower than those in their Western counterparts. However, in the Chinese patients in Hong Kong, heterozygous FH appears to manifest in a way similar to that seen in Western countries or Japan. We studied sequence variations in the promoter and coding regions of the 18 exons of the LDL receptor gene in 30 Chinese FH patients. Eighteen mutations were identified in 21 patients scattered in the promoter and 10 exons. Eleven of them were first found in this study. We also found 6 polymorphisms with allelic frequencies different from those in whites but similar to the Japanese, indicating some isolation between white and Oriental populations. A total of 29 mutations in the LDL receptor gene are now known in the Chinese. There is no definite common mutation due to a founder effect. Meanwhile, there were no detectable LDL receptor gene mutations in 9 clinically diagnosed FH patients in whom the R3500Q mutation in apolipoprotein B had also been excluded. The gene defects leading to the FH phenotype in these patients may occur somewhere else in the apolipoprotein B or other related genes, or even in the noncoding sequences of the LDL receptor gene.

Adolescent↗
PubMed1998

Chronic refractory tibia osteomyelitis treated with adjuvent hyperbaric oxygen: a preliminary report.

BACKGROUND: Refractory osteomyelitis is a serious disease that fails to respond to aggressive medical and surgical treatment. A plethora of alternative therapies have evolved. Hyperbaric oxygen has been proven to enhance bone and soft tissue healing in many in vitro and in vivo studies. This article presents the preliminary results of adjunctive hyperbaric oxygen therapy in patients with refractory osteomyelitis. MATERIALS AND METHODS: Fifteen patients who were diagnosed with refractory tibia osteomyelitis were treated prospectively with adjunctive hyperbaric oxygen therapy, aggressive surgical debridement, and parenteral antibiotic treatment. The effectiveness was evaluated with an average follow-up of 17.2 months. RESULTS: The hyperbaric oxygen therapy averaged 26 daily sessions. Successful treatment was achieved in 13 patients (86%). The mean length of treatment was 45 days. The preliminary results are comparable with other series. CONCLUSION: Hyperbaric oxygen is effective as an adjunct to aggressive medical and surgical management in refractory osteomyelitis. A precise clinical staging system for patient selection and treatment organization is imperative to successful outcome.

Adolescent↗
PubMed1997

The coding of head orientations in neurons of bilateral vestibular nuclei of cats after unilateral labyrinthectomy: response to off-vertical axis rotation.

In decerebrate cats that had been acutely hemilabyrinthectomized (HL), the extracellular activities of vestibular nuclear neurons on the lesioned and labyrinth-intact sides were studied during constant-velocity off-vertical axis rotations (OVAR) in the clockwise (CW) and counterclockwise (CCW) directions (at 10 degrees tilt). Over the range of 1.75-15 degrees/s, two types of neuronal responses were identified on both sides. Some neurons showed symmetric and velocity-stable bidirectional response sensitivity (delta defined as the CW gain over the CCW gain) while other neurons exhibited asymmetric and velocity-variable delta. The mathematically derived gain tuning ratios of these two groups of neurons were within the range of one-dimensional and two-dimensional neurons respectively. The best response orientations in one-dimensional neurons and the orientations of the maximum response vector, S(max), in two-dimensional neurons were found to point in all directions on the horizontal plane. On the labyrinth-intact side, both the one-dimensional and two-dimensional neurons showed asymmetry in the neuron numbers and/or the response gains between the two roll quadrants as well as between the two pitch quadrants. In addition, both the neuron number and gain were significantly higher for neurons in the head-down/ipsilateral-side-down half-circle than those in the head-up/contralateral-side-down half-circle. None of the aforementioned asymmetries was observed on the lesioned side. That a comparable pattern of distribution was observed in the one-dimensional and two-dimensional neurons suggests that these neurons maintain a common spatial reference frame in encoding head orientational signals arising from the ipsilateral and contralateral otoliths. Furthermore, a predominance of two-dimensional neurons that exhibited a greater gain with CW rotations was observed on both sides of HL cats. Of the response dynamics observed amongst neurons on the two sides of HL cats, no difference was found with regard to the response gain and the pattern of response lead. However, a difference in response lag was observed between neurons on the two sides of HL cats. These suggest that there is a segregation of otolithic signals to reach the ipsilateral and contralateral vestibular nuclei. Taken together, the present study demonstrates that one-dimensional and two-dimensional neuronal responses could be elicited with inputs arising solely from the ipsilateral or contralateral otoliths. The observed orientational tuning and the CW-CCW asymmetry to bidirectional rotation may provide the essential directional coding of head orientations. Further, the imbalance of spatial/dynamic response patterns between the bilateral vestibular nuclei following the restriction of otolith inputs by HL implies that converging otolithic inputs from the bilateral labyrinths are essential for producing the neuronal responses in control animals. The results are also discussed in terms of the possible contribution of the various neural asymmetries between neuronal subpopulations in the bilateral vestibular nuclei to the behavioral symptoms accompanying acute HL.

Animals↗
PubMed1997

Influence of landfill factors on plants and soil fauna-an ecological perspective.

An ecological study was conducted on two landfill sites in Hong Kong. Both sites were contaminated by landfill gas and leachate, as indicated by the high concentrations of CH(4) and CO(2) and the presence of high concentration of NH(4)-N in the cover soil layer. Their plant diversity and performance, as well as the soil and litter animals, were compared with three derelict sites as references. The landfill sites had higher plant coverage and plant diversity, and higher densities of soil and litter animals than the reference sites. Similarly, the microbial activities at the landfill sites were higher than those at reference sites. The results showed that the landfill sites possessed an effective food web, starting from microbes to macroinvertebrates. Woodland establishment seems feasible at these landfill sites, and natural succession appears to take place at a higher rate at these landfill sites when compared with the reference sites.

Journal Article↗