Signaling by the TNF receptor superfamily and T cell homeostasis.
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Animals↗
Biomedical subjects
K F Chan
Publications and source records attributed to K F Chan.
Dynamics of pulsed holmium:YAG laser photocoagulation of albumen.
The pulsed holmium:YAG laser (lambda = 2.12 microm, tau(p) = 250 micros) has been investigated as a method for inducing localized coagulation for medical procedures, yet the dynamics of this process are not well understood. In this study, photocoagulation of albumen (egg white) was analysed experimentally and results compared with optical-thermal simulations to investigate a rate process approach to thermal damage and the role of heat conduction and dynamic changes in absorption. The coagulation threshold was determined using probit analysis, and coagulum dynamics were documented with fast flash photography. The nonlinear computational model, which included a Beer's law optical component, a finite difference heat transfer component and an Arrhenius equation-based damage calculation, was verified against data from the literature. Moderate discrepancies between simulation results and our experimental data probably resulted from the use of a laser beam with an irregular spatial profile. This profile produced a lower than expected coagulation threshold and an irregular damage distribution within a millisecond after laser onset. After 1 ms, heat conduction led to smoothing of the coagulum. Simulations indicated that dynamic changes in absorption led to a reduction in surface temperatures. The Arrhenius equation was shown to be effective for simulating transient albumen coagulation during pulsed holmium:YAG laser irradiation. Greater understanding of pulsed laser-tissue interactions may lead to improved treatment outcome and optimization of laser parameters for a variety of medical procedures.
Albumins↗
Free electron laser lithotripsy: threshold radiant exposures.
PURPOSE: To determine the threshold radiant exposures (J/cm2) needed for ablation or fragmentation as a function of infrared wavelengths on various urinary calculi and to determine if there is a relation between these thresholds and lithotripsy efficiencies with respect to optical absorption coefficients. MATERIALS AND METHODS: Human calculi composed of uric acid, calcium oxalate monohydrate (COM), cystine, or magnesium ammonium phosphate hexahydrate (MAPH) were used. The calculi were irradiated in air with the free electron laser (FEL) at six wavelengths: 2.12, 2.5, 2.94, 3.13, 5, and 6.45 microm. RESULTS: Threshold radiant exposures increased as optical absorption decreased. At the near-infrared wave-lengths with low optical absorption, the thresholds were >1.5 J/cm2. The thresholds decreased below 0.5 J/cm2 for regions of high absorption for all the calculus types. Thresholds within the high-absorption regions were statistically different from those in the low-absorption regions, with P values much less than 0.05. CONCLUSIONS: Optical absorption coefficients or threshold radiant exposures can be used to predict lithotripsy efficiencies. For low ablation thresholds, smaller radiant exposures were required to achieve breakdown temperatures or to exceed the dynamic tensile strength of the material. Therefore, more energy is available for fragmentation, resulting in higher lithotripsy efficiencies.
Differential Threshold↗
Sex differences in opinion towards mental illness of secondary school students in Hong Kong.
Sex differences in social attitudes have been well documented. Women hold more positive attitudes toward mental illness than men do. This paper reports on the effect of sex differences in a study of secondary school students' opinions about mental illness in Hong Kong. A total of 2,223 secondary school students, drawn by random sample, completed a 45-item questionnaire on Opinion about Mental Illness in Chinese Community (OMICC) with a six-point Likert Scale. Individual items with weak correlations were eliminated, leaving 33 items for analysis (Cronbach's Alpha = .866). Using factor analysis six factors were identified. These include: Benevolence, Separatism, Stereotyping, Restrictiveness, Pessimistic Prediction and Stigmatization. Results showed that girls scored higher regarding benevolence. Boys were found to have more stereotyping, restrictive, pessimistic and stigmatizing attitudes towards mental illness.
Adolescent↗
Holmium:YAG laser lithotripsy: A dominant photothermal ablative mechanism with chemical decomposition of urinary calculi.
BACKGROUND AND OBJECTIVE: Evidence is presented that the fragmentation process of long-pulse Holmium:YAG (Ho:YAG) lithotripsy is governed by photothermal decomposition of the calculi rather than photomechanical or photoacoustical mechanisms as is widely thought. The clinical Ho:YAG laser lithotriptor (2.12 microm, 250 micros) operates in the free-running mode, producing pulse durations much longer than the time required for a sound wave to propagate beyond the optical penetration depth of this wavelength in water. Hence, it is unlikely that shock waves are produced during bubble formation. In addition, the vapor bubble induced by this laser is not spherical. Thus the magnitude of the pressure wave produced at cavitation collapse does not contribute significantly to lithotripsy. STUDY DESIGN/MATERIALS AND METHODS: A fast-flash photography setup was used to capture the dynamics of urinary calculus fragmentation at various delay times following the onset of the Ho:YAG laser pulse. These images were concurrently correlated with pressure measurements obtained with a piezoelectric polyvinylidene-fluoride needle-hydrophone. Stone mass-loss measurements for ablation of urinary calculi (1) in air (dehydrated and hydrated) and in water, and (2) at pre-cooled and at room temperatures were compared. Chemical and composition analyses were performed on the ablation products of several types of Ho:YAG laser irradiated urinary calculi, including calcium oxalate monohydrate (COM), calcium hydrogen phosphate dihydrate (CHPD), magnesium ammonium phosphate hexahydrate (MAPH), cystine, and uric acid calculi. RESULTS: When the optical fiber was placed perpendicularly in contact with the surface of the target, fast-flash photography provided visual evidence that ablation occurred approximately 50 micros after the initiation of the Ho:YAG laser pulse (250-350 micros duration; 375-400 mJ per pulse), long before the collapse of the cavitation bubble. The measured peak acoustical pressure upon cavitation collapse was negligible (< 2 bars), indicating that photomechanical forces were not responsible for the observed fragmentation process. When the fiber was placed in parallel to the calculus surface, the pressure peaks occurring at the collapse of the cavitation were on the order of 20 bars, but no fragmentation occurred. Regardless of fiber orientation, no shock waves were recorded at the beginning of bubble formation. Ablation of COM calculi (a total of 150 J; 0.5 J per pulse at an 8-Hz repetition rate) revealed different Ho:YAG efficiencies for dehydrated calculus, hydrated calculus, and submerged calculus. COM and cystine calculi, pre-cooled at -80 degrees C and then placed in water, yielded lower mass-loss during ablation (20 J, 1.0 J per pulse) compared to the mass-loss of calculi at room temperature. Chemical analyses of the ablated calculi revealed products resulting from thermal decomposition. Calcium carbonate was found in samples composed of COM calculi; calcium pyrophosphate was found in CHPD samples; free sulfur and cysteine were discovered in samples composed of cystine samples; and cyanide was found in samples of uric acid calculi. CONCLUSION: These experimental results provide convincing evidence that long-pulse Ho:YAG laser lithotripsy causes chemical decomposition of urinary calculi as a consequence of a dominant photothermal mechanism.
Holmium↗
Holmium: YAG lithotripsy: photothermal mechanism.
OBJECTIVE: A series of experiments were conducted to test the hypothesis that the mechanism of holmium:YAG lithotripsy is photothermal. METHODS AND RESULTS: To show that holmium:YAG lithotripsy requires direct absorption of optical energy, stone loss was compared for 150 J Ho:YAG lithotripsy of calcium oxalate monohydrate (COM) stones for hydrated stones irradiated in water (17+/-3 mg) and hydrated stones irradiated in air (25+/-9 mg) v dehydrated stones irradiated in air (40+/-12 mg) (P < 0.001). To show that Ho:YAG lithotripsy occurs prior to vapor bubble collapse, the dynamics of lithotripsy in water and vapor bubble formation were documented with video flash photography. Holmium:YAG lithotripsy began at 60 microsec, prior to vapor bubble collapse. To show that Ho:YAG lithotripsy is fundamentally related to stone temperature, cystine, and COM mass loss was compared for stones initially at room temperature (approximately 23 degrees C) v frozen stones ablated within 2 minutes after removal from the freezer. Cystine and COM mass losses were greater for stones starting at room temperature than cold (P < or = 0.05). To show that Ho:YAG lithotripsy involves a thermochemical reaction, composition analysis was done before and after lithotripsy. Postlithotripsy, COM yielded calcium carbonate; cystine yielded cysteine and free sulfur; calcium hydrogen phosphate dihydrate yielded calcium pyrophosphate; magnesium ammonium phosphate yielded ammonium carbonate and magnesium carbonate; and uric acid yielded cyanide. To show that Ho:YAG lithotripsy does not create significant shockwaves, pressure transients were measured during lithotripsy using needle hydrophones. Peak pressures were <2 bars. CONCLUSION: The primary mechanism of Ho:YAG lithotripsy is photothermal. There are no significant photoacoustic effects.
Analysis of Variance↗
Colchicine-induced myopathy and neuropathy.
Myopathy and neuropathy that have been induced by colchicine have been described only occasionally, although colchicine is a widely used drug. We describe a case of colchicine-induced myopathy and neuropathy in an 84-year-old woman who had renal impairment. Results from a muscle biopsy showed characteristic vacuolar myopathy and autophagic vacuoles. The cessation of medication resulted in a marked improvement of myopathy.
Journal Article↗
Musculoskeletal pain clinic in Singapore--sacroiliac joint somatic dysfunction as cause of buttock pain.
Buttock pain was a predominant symptom in a series of patients seen with recalcitrant "backache" in the author's pain clinic which has a musculoskeletal emphasis. Assessment suggested the sacroiliac joint as the culprit pain generator and patients underwent confirmatory testing which included fluoroscopy-guided intra-articular injections of lignocaine and steroid along with combined therapeutic modalities of oral analgesics, physical therapy, manual medicine techniques and ergonomic assessments. Two case reports illustrate this condition which is probably under-recognised and inadequately addressed locally.
Adult↗
Transcriptional regulation of transferrin receptor expression during phorbol-ester-induced HL-60 cell differentiation. Evidence for a negative regulatory role of the phorbol-ester-responsive element-like sequence.
The mechanism involved in the regulation of transferrin receptor (TfR) expression during phorbol-ester-induced HL-60 cell differentiation was investigated. The mRNA of the TfR was constitutively expressed in proliferating HL-60 cells. Treatment of the cells with phorbol 12-myristate 13-acetate (PMA) for 24 h resulted in a gradual decrease in the expression of the TfR mRNA. Nuclear run-on assays revealed that the transcription of the TfR gene was inhibited by prior treatment of cells with PMA. The effect of PMA on the binding of nuclear proteins to the TfR gene promoter region was then investigated. Based on sequence similarity and previous footprinting data, the promoter region of the TfR gene seems to contain a sequence like that of the phorbol-ester-responsive element (TRE). Our results showed that the binding of nuclear extracts to the TfR gene promoter region containing the TRE-like sequence was increased in PMA-treated cells. This binding activity could be abolished by prior incubation of the nuclear extracts with a synthetic oligonucleotide containing the consensus TRE sequence. In vitro transcription assays revealed that prior incubation of the nuclear extracts of PMA-treated cells with excess consensus TRE oligonucleotide enhanced the gene transcription driven by the TfR gene promoter. These findings suggest that the TRE-like element may play a role in the inhibition of TfR gene transcription.
Binding Sites↗
Transverse myelopathy in SLE: clinical features and functional outcomes.
The objective of the study was to examine the clinical features of lupus patients who present with transverse myelopathy (TM) and ascertain functional outcomes when treated early with high dose corticosteroids and/or cyclophosphamide. Case records of nine patients who developed a total of 14 episodes of TM were retrospectively studied. All the patients were female and their ages ranged from 21 to 59 years. Nine episodes of paraparesis, three of tetraparesis, one of numbness and one of neurogenic bladder were reported early in the diagnosis of SLE (median of two years). Neurogenic bowel and bladder and presence of ANA and ds-DNA were invariable. Urodynamics assessment in six patients showed abnormal detrusor behavior in all. CT scans and myelograms were uninformative and CSF studies were normal. ESR and complement levels were insensitive as markers of disease activity. The treatment regimens included pulses of methylprednisolone and/or cyclophosphamide followed by prednisolone and high dose prednisolone from onset. The functional outcomes were uniformly good-with independent ambulation in all except three (who needed assistive devices) and improvement of motor scores. Acute hospital stays were short (range of three to 45 days) whilst only two were referred for inpatient rehabilitation. Bladder abnormalities persisted despite motor recovery and would require long-term review.
Adult↗
Effects of protein kinase modulators on transferrin receptor expression in human leukaemic HL-60 cells.
The mRNA of transferrin receptor (TfR) is constitutively expressed in proliferating human leukaemic HL-60 cells. Treatment of HL-60 cells with phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, or dibutyryl-cyclic AMP (dbcAMP), a protein kinase A (PKA) activator, resulted in a 90% decrease in the level of TfR mRNA. Inhibition of TfR mRNA expression induced by 10 nM PMA and 100 microM dbcAMP was abolished by prior incubation of cells with 0.1-1.0 microM GF109203X, a PKC-specific inhibitor, and 1-10 microM H-89, a PKA-specific inhibitor, respectively. The blocking effects of GF109203X and H-89 were dose-dependent and complete at the highest concentrations of the inhibitors used. Although treatment of cells with GF109203X or H-89 alone did not alter the constitutive expression of TfR mRNA, incubation of cells with 30-100 nM staurosporine, a wide-spectrum protein kinase inhibitor, resulted in suppression of the constitutive expression of TfR mRNA in a dose-dependent manner. These results suggest that (i) the down-regulation of TfR mRNA expression during the differentiation of HL-60 cells can be mediated by activation of either PKC or PKA; (ii) the constitutive expression of TfR mRNA in proliferating HL-60 cells is staurosporine-sensitive and is probably maintained by protein kinase(s) other than PKC and PKA.
Alkaloids↗
Ruptured intracranial mycotic aneurysm: a rare cause of intracranial hemorrhage.
Intracranial mycotic aneurysm is a rare complication in patients with infective endocarditis occurring in about 2% to 10% of cases. Although the risk of rupture is about 1.7%, it is usually a catastrophic event with a fatality rate of 80%. Neurological deficits secondary to cortical involvement are common, given the frequency of intralobar hemorrhage. We report two cases of intracerebral hemorrhage caused by ruptured intracranial mycotic aneurysms. Both had involvement of the right frontoparietal lobes with resultant left hemiparesis, left homonymous hemianopia, and impairments of cognition and perceptual function. Despite intensive rehabilitation, their functional outcomes were less than satisfactory as they needed assistance in self-care activities and mobility on discharge.
Adult↗
"Great mimicry" in a patient with tetraparesis: a case report.
The patient is a 63-year-old Chinese man who presented with tetraparesis and urinary incontinence. The initial diagnosis was cord compression from cervical spondylosis. The patient relapsed 3 months after cervical laminectomy. The transverse myelitis picture, left optic atrophy and suggestive brainstem evoked potentials led to treatment of a presumptive demyelinating process. The presence of vitiligo, however, led to detection of high titers of antinuclear antibodies (ANA) and presence of anti-nonhistone antibodies. The patient was then diagnosed to have a lupus (SLE)-like disease, which has not fully evolved. He was prescribed pulsed cyclophosphamide and prednisolone with significant gains both neurologically and functionally up to 1 year of follow-up. This report highlights the befuddling impact the disease process have on the clinicians in terms of diagnosis, treatment, and prognosis. That it can occur in men in the seventh decade of life heightens the need for awareness in our approach to the myelopathic patient.
Cervical Vertebrae↗
Functional outcome in young strokes.
Fifty-seven young stroke patients (aged 45 years and below) admitted to a rehabilitation centre were assessed for underlying risk factor/aetiology and functional outcome after rehabilitation. The mean age was 37.2 +/- 6.3 years and the mean length of stay in the rehabilitation ward 38.3 +/- 19.9 days. There were 37 (64.9%) haemorrhagic and 20 (35.1%) ischaemic strokes. Hypertension was the single most important risk factor accounting for 49.1% of all strokes. Vascular abnormalities (arteriovenous malformation, mycotic aneurysm, vasculitis and Moya-moya disease) and cardiogenic embolism secondary to rheumatic valvular heart disease were also significant causes. There was significant improvement in functional status--activities of daily living (ADL) and mobility--after rehabilitation, the mean Functional Status score improving from 9.76 +/- 2.2 on admission to 5.07 +/- 1.95 on discharge (P < 0.01). Higher ADL and mobility function and upper and lower limb motor power of grade 3 and above on admission, absence of dysphasia, left hemiplegia, age less than 40 years and rehabilitation stay of less than 28 days were associated with better functional outcome whilst sex, nature and site of stroke, and length of stay in the acute ward had no significant bearing.
Activities of Daily Living↗
Detrusor hyperreflexia in strokes.
Urodynamic evaluation via water cystometry was undertaken in 27 patients from 12 to 120 days after cerebrovascular accidents. Seven patients had urinary symptoms--five with urge incontinence, one with frequency and one with sensation of incomplete bladder emptying. The remaining 20 were asymptomatic. Cystometry revealed normal bladder function in 15 patients (55.6%), detrusor areflexia in one patient (3.7%) and detrusor hyperreflexia in 11 patients (40.7%). Of the 11 patients with detrusor hyperreflexia, six (54.5%) were asymptomatic and the remaining five (45.5%) had urge incontinence. The former group had a statistically significant higher first sensation and functional cystometric capacity than the latter. Urge incontinence was also found to be an accurate predictor of detrusor hyperreflexia.
Adult↗
[Immunotherapy of the malignant tumors of central nervous system].
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Central Nervous System Neoplasms↗
High-performance capillary electrophoresis of gangliosides.
Gangliosides are sialic acid-containing glycosphingolipids. In aqueous media, these glycolipids have been shown to exist as stable micelles. Ganglioside micelles could be analyzed by high-performance zonal capillary electrophoresis in uncoated fused-silica capillaries within 10 min. The mass sensitivity determined by monitoring the absorption of ultraviolet light at 195 nm was in the order of 10(-11) mol. Increasing the pH of the running buffer from 3.0 to 7.4 or the voltage from 10 to 30 kV increased the relative mobilities of gangliosides. By contrast, increasing the ionic strength of the buffer decreased the migration and broadened the elution peak widths of gangliosides. Ganglioside* micelles including GM1, GD1b, and GT1b were resolved into separate peaks by capillary electrophoresis at physiological pH shortly after mixing. Upon prolonged incubation, the ganglioside peaks merged to form a single species. The fusion process was temperature-dependent. At 50 degrees C, formation of mixed micelles between polysialogangliosides GD1b and GT1b was complete within 30 min. In contrast, no fusion of the ganglioside peaks was observed at 0 degrees C even after 75 h. Formation of mixed micelles between GD1b and other polysialogangliosides including GD1a, GT1b, and GQ1b at 37 degrees C required 1.5, 3.0, and 2.0 h, respectively. Formation of mixed micelles between monosialoganglioside GM1 and polysialogangliosides were 6- to 36-fold slower. No fusion was observed between monosialogangliosides GM1 and GM2 after 2 days of incubation. These findings indicate that polysialogangliosides may have higher propensities than monosialoganglioside to form mixed micelles.
Electrophoresis↗
In vitro changes in the fine structure and protein composition of light myelin fractions isolated from guinea pig brain.
To find out if in vitro maintenance produces changes in the electron microscopic appearance, protein composition and phosphorylation properties of guinea pig CNS myelin fractions, we incubated them for 10 min, 4 hr, 24 hr, and 48 hr in phosphate-buffered saline (pH 7.4) or in 20 mM Hepes, 2 mM EDTA, 0.5 mM EGTA, 0.5 mM dithiothreitol, and 20 mM NaCl at 4 and 30 degree C. Aliquots were processed for electron microscopic study, were analyzed for protein content by gel electrophoresis, and were assayed for endogenous protein phosphorylation. Before incubation, electron micrographs of fractions contained two types of multilamellar whorls with the periodicity of CNS myelin sheaths. The first type of whorl was separated from nearby whorls; the other type had surface lamellae that were connected to other multilayered membrane fragments. After incubation at 4 degree C for 24 hr, the number of both types of multilamellar whorls in micrographs had increased approximately 3- to 4- fold. Counts per unit area showed that the observed increase was both time- and temperature-dependent. In aliquots studied by gel electrophoresis, only minor degradation of myelin proteins was observed. The endogenous protein phosphorylation properties of the myelin fragments also remained functional, suggesting that the activities of protein phosphotransferases were not altered. We conclude that the incubation conditions described here favor interactions of proteins and lipids that lead to the formation of multilayered aggregates of CNS myelin membranes.
Animals↗