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Biomedical subjects

S Chow

Publications and source records attributed to S Chow.

At least 37 records · Page 2Linked to original sources
PubMed1999

A comparison in individual murine tumors of techniques for measuring oxygen levels.

PURPOSE: To investigate the relationship between different techniques for measuring oxygen levels in a murine tumor model. METHODS AND MATERIALS: Using the murine fibrosarcoma line KHT-C, five techniques of measuring oxygen levels-the Eppendorf pO2 Histograph, EF5 binding, the comet assay, a paired survival assay, and an in vivo growth delay assay-were assessed. In these experiments, three or more techniques were applied in different combinations to measure the oxygen levels in individual tumors. RESULTS: Statistically significant correlations were observed between the hypoxic proportions calculated from the paired survival assay with those from EF5 binding. The comet assay was found to have a statistically significant correlation with the paired survival analysis and the growth delay analysis. No statistically significant correlation was found between the Eppendorf pO2 Histograph measurements and those from the other techniques, although there were weak correlations with the paired survival assay and EF5 binding. For technical reasons, a comparison was not made between EF5 binding and the growth delay assay. CONCLUSIONS: The correlations found between EF5 binding and the comet assay with the radiobiological assays suggest that these techniques have potential for predicting outcome following radiation treatment. The lack of correlation seen between the pO2 Histograph data and the radiobiological assays is in contrast to results from early clinical trials.

Animals↗
PubMed1999

Induction of microtubule-associated protein 1B expression in Schwann cells during nerve regeneration.

Microtubule-associated protein 1B (MAP1B) is expressed at high levels during development of the nervous system and is localized primarily in neurons while specific phosphorylated isoforms of MAP1B are localized exclusively in growing axons. The levels of MAP1B are down regulated in most regions of the adult CNS, but remain high in neurons and axons of the PNS. This study demonstrates that the expression of MAP1B is induced in adult Schwann cells following sciatic nerve lesion and regeneration. High levels of both mRNA and the MAP1B protein were detected in Schwann cells associated with the axotomized distal stump. Expression of MAP1B was also observed in cultured primary Schwann cells from neonatal rats. The properties of the MAP1B protein in cultured Schwann cells were further characterized by Western blot analysis using specific antibodies that recognize the N-terminal, middle and C-terminal domains of MAP1B. All of these antibodies detected a protein of 320-340 kDa demonstrating that MAP1B expressed by Schwann cells is very similar, or identical, to MAP1B expressed by neurons. The phosphorylation of MAP1B in Schwann cells was also studied using monoclonal antibodies (mAb) that recognize specific phosphorylation epitopes. The results indicated that the expression of MAP1B in Schwann cells exhibited a differential phosphorylation state that was recognized by mAb 1B6 but not by other mAbs, including 1B-P, 150 and RT97, that recognize phosphorylated MAP1B in growing axons. We therefore conclude that MAP1B is expressed in Schwann cells during both development and axonal regeneration, suggesting that the developmental pattern of MAP1B in these cells is recapitulated in adult Schwann cells during the early stages of regeneration and remyelination of injured peripheral axons. The presence of MAP1B in Schwann cells may support morphological changes of these cells, particularly the formation of processes prior to their differentiation into myelin forming Schwann cells.

Animals↗
PubMed1999

Total skin electron beam therapy with or without adjuvant topical nitrogen mustard or nitrogen mustard alone as initial treatment of T2 and T3 mycosis fungoides.

PURPOSE: To compare the efficacy of total skin electron beam therapy (TSEBT) with or without adjuvant topical nitrogen mustard (+/- HN2) with topical nitrogen mustard (HN2) alone as initial management of T2 and T3 mycosis fungoides (MF). METHODS AND MATERIALS: A retrospective analysis of 148 patients presenting to Stanford from January, 1970 through January, 1995 within 4 months of pathologic diagnosis of MF. Fifty-five patients with T2 and 27 with T3 disease received TSEBT +/- HN2. Fifty-four patients with T2 and 12 with T3 disease received HN2 alone. Boosts with radiotherapy were usually administered to cutaneous tumors of patients with T3 disease. RESULTS: TSEBT +/- HN2 yielded significantly higher complete response (CR) rates than did HN2 alone in patients with T2 and T3 disease (76% vs 39%, p = 0.03 for T2, and 44% vs 8%, p < 0.05 for T3, respectively). In T2 disease, treatment with adjuvant HN2 was associated with a longer freedom from relapse following TSEBT when compared to observation following a CR to TSEBT (p = 0.068). However, no significant differences in survival were observed for different management programs for T2 or T3 disease. In T2 disease, both TSEBT and HN2 were as effective as salvage therapy as when utilized as initial therapy. However, salvage therapy in T3 disease was rarely effective. Limited tumor involvement in T3 disease did not correlate with improved survival compared to more generalized tumorous disease. MF contributed to 27% and 68% of deaths in patients with T2 and T3 disease, respectively. CONCLUSION: Because of high response rates, management of significantly symptomatic or extensive T2 MF should include TSEBT, and adjuvant HN2 should be administered after a CR to TSEBT. Patients with T2 disease who fail TSEBT or HN2 can be salvaged with the other modality. TSEBT is also an effective treatment for T3 disease. The small subset of patients with limited T3 disease may also be treated with HN2 and local radiotherapy to the tumors. Further investigations are necessary to improve the overall outcome for T3 mycosis fungoides.

Administration, Topical↗
PubMed1999

Clinical characteristics and long-term outcome of patients with generalized patch and/or plaque (T2) mycosis fungoides.

OBJECTIVES: To study the long-term results of treatment of patients with generalized patch and/or plaque mycosis fungoides and to identify clinical characteristics predictive of survival and response to treatment. DESIGN: A single-center, 35.5-year retrospective cohort analysis. SETTING: Private referral medical center. PATIENTS: One hundred seventy-six patients with generalized patch and/or plaque (T2) mycosis fungoides. MAIN OUTCOME MEASURES: Long-term actuarial survival and freedom-from-relapse results as calculated by the Kaplan-Meier method. RESULTS: The long-term (35.5-year) survival of patients with T2 mycosis fungoides is worse than the expected survival of a race-, age-, and sex-matched control population (P<.001). The median survival of the T2 group is 11.7 years. Patients younger than 58 years (median age) at presentation have a more favorable overall and disease-specific survival than the patients who are 58 years or older (P<.001 vs P<.025). Patient sex or race had no significant effect on overall survival. Patients who presented with palpable clinically significant lymph nodes (stage IIA) had long-term survival results similar to those without lymphadenopathy (stage IB), despite improved freedom-from-relapse outcome for patients with stage IB. Twenty-four percent of patients who progressed to more advanced disease had a lower complete response rate to initial therapy than did other patients (21% vs 65%) (P<.001). Patients who received total skin electron beam therapy had a better complete response rate than patients treated with topical mechlorethamine hydrochloride alone; the relapse-free results were superior in patients with a total dose of 30 Gy or higher and in patients who received topical mechlorethamine as adjuvant therapy following total skin electron beam therapy. Despite differences in freedom-from-relapse results among different treatment groups, long-term overall or disease-specific survivals were not significantly different. CONCLUSIONS: A significant proportion (24%) of patients with generalized patch and/or plaque (T2) mycosis fungoides experience disease progression to a more advanced clinical stage, and nearly 20% eventually die of the disease. Younger patients have a more favorable disease-specific long-term outcome than patients who are older. Presence of lymphadenopathy (stage IIA) at diagnosis does not predict worse long-term survival outcome. Clinical features predictive of disease progression include initial lymphadenopathy (stage IIA) and lack of complete response to initial treatment. Despite superior complete response rate to a 30-Gy or higher dose of total skin electron beam therapy, topical mechlorethamine proves to be a cost-effective initial treatment for patients with T2 disease. The concept of an adjuvant therapy after irradiation is appealing, although it may not lead to improved long-term survival.

Adult↗
PubMed1999

Prevention of immune dysfunction and vitamin E loss by dehydroepiandrosterone and melatonin supplementation during murine retrovirus infection.

Female C57BL/6 mice infected with the LP-BM5 leukaemia retrovirus developed murine acquired immune-deficiency syndrome (AIDS). Dehydroepiandrosterone (DHEA) and melatonin (MLT) modify immune dysfunction and prevent lipid peroxidation. We investigated whether DHEA and MLT could prevent immune dysfunction, excessive lipid peroxidation, and tissue vitamin E loss induced by retrovirus infection. Retrovirus infection inhibited the release of T helper 1 (Th1) cytokines, stimulated secretion of Th2 cytokines, increased hepatic lipid peroxidation, and induced vitamin E deficiency. Treatment with DHEA or MLT alone, as well as together, largely prevented the reduction of B- and T-cell proliferation as well as of Th1 cytokine secretion caused by retrovirus infection. Supplementation also suppressed the elevated production of Th2 cytokines stimulated by retrovirus infection. DHEA and MLT simultaneously reduced hepatic lipid peroxidation and prevented vitamin E loss. The use of DHEA plus MLT was more effective in preventing retrovirus-induced immune dysfunction than either DHEA or MLT alone. These results suggest that supplementation with DHEA and MLT may prevent cytokine dysregulation, lipid oxidation and tissue vitamin E loss induced by retrovirus infection. Similarly, hormone supplementation also modified immune function and increased tissue vitamin E levels in uninfected mice.

Animals↗
PubMed1999

Measuring the inappropriate utilization of accident and emergency services?

Accident and Emergency (A&E) departments are increasingly popular venues for primary care, causing a serious threat to healthcare quality. This paper reports the development of a comprehensive research method for identifying primary care patients attending A&E. Patients were randomly selected from the four A&E departments across different time periods and different regions in Hong Kong. The definition of GP cases was based on a retrospective record review conducted by a panel of emergency physicians using the standard laid down by the Hong Kong College of Family Physicians. The patients sampled were similar in sex and age distribution to A&E attendees for the whole territory. The level of GP cases was found to be 57 per cent, with a significantly higher proportion of patients in the younger age group. The high level of use reflects the lack of a well co-ordinated development of primary care services and interfacing with secondary care.

Adolescent↗
PubMed1998

Analysis of multiplexed short tandem repeat (STR) systems using capillary array electrophoresis.

The profiling of polymorphic short tandem repeat (STR) markers is being applied to human identification, parentage testing and genetic mapping. Reliable genotyping of these markers is facilitated by polymerase chain reaction (PCR) amplification and high-resolution electrophoretic separation. Capillary array electrophoresis (CAE) offers very rapid, high-resolution separation of the amplified DNA and potential for automated sample processing not realized employing conventional slab-gel electrophoresis. The use of CAE to type DNA samples amplified at 11 genetic loci in multiplex profiles is presented. Two sets totaling 208 samples were amplified in a multiplex fashion using AmpFlSTR-Blue or AmpFlSTR-Green I and analyzed in a blind study using CAE. With the exception of one sample, the CAE genotyping results were in complete agreement with results obtained using a single-capillary system or two slab-gel electrophoresis systems. The sample, genotype TH01 7/10, migrated similar to TH01 6.3/9.3 allele sizes, which suggested a potential band migration shift. The recommended approach to such an observation is to analyze the sample again. The sample was rerun and correct genotype verified. Allelic ladder samples were analyzed multiple times by CAE to determine sizing accuracy and precision. The sizing of over 240 allelic ladder samples yielded an average within-run precision of +/- 0.13 bp and between-run precision of +/- 0.21 bp for fragments up to 350 bp. The CAE protocols permit processing of up to 96 multiplex STR samples in under 70 min.

Alleles↗
PubMed1998

Antileukemic action of buthionine sulfoximine: evidence for an intrinsic death mechanism based on oxidative stress.

The glutathione-depleting agent buthionine sulfoximine (BSO) was found to be toxic to some AML blast populations. This toxicity was manifested as the appearance of high levels of reactive oxygen generation in GSH-depleted cells, and later by the loss of mitochondrial membrane potential and an increase in intracellular calcium. Striking heterogeneity in BSO sensitivity was observed in a series of four human AML cell lines, and in fresh leukemic blasts obtained from eight AML patients. In some cases, toxicity was seen at BSO concentrations as low as 1 microM; approximately 100-fold less than the plasma levels achieved in patients treated with BSO as a drug resistance reversing agent. Based on these results we propose that some AML blast populations are unusually dependent on GSH-based antioxidant mechanisms, due to high intrinsic rates of reactive oxygen generation. The mitochondrial respiratory chain is the most likely source of this reactive oxygen. Because toxicity is seen at clinically achievable concentrations of BSO, this agent might have antileukemic activity in patients.

Adult↗
PubMed1998

Management of occluded biliary Wallstents.

BACKGROUND: Wallstents (Schneider Stent, Inc., USA) used for the palliation of malignant biliary strictures, although associated with prolonged patency, can occlude. There is no consensus regarding the optimal management of Wallstent occlusion. AIMS: To evaluate the efficacy of different endoscopic methods for managing biliary Wallstent occlusion. METHODS: A multicentre retrospective study of patients managed for a biliary Wallstent occlusion. RESULTS: Data were available for 38 patients with 44 Wallstent occlusions, all of which had initial endoscopic management. Twenty four patients had died and 14 were alive after a median follow up of 231 (30-1095) days following Wallstent occlusion. Occlusions were managed by insertion of another Wallstent in 19, insertion of a plastic stent in 20, and mechanical cleaning in five. Endoscopic management was successful in 43 (98%). Following management of the occlusion, bilirubin decreased from 6.0 (0.5-34.3) to 2.1 (0.2-27.7) mg/100 ml (p < 0.05). No complications occurred. The median duration of second stent patency was 75 days (95% confidence interval 43 to 107) after insertion of another Wallstent, 90 days (71 to 109) after insertion of a plastic stent, and 34 days (30 to 38) after mechanical cleaning (NS). The respective median survivals were 70 days (22-118), 98 days (54-142), and 34 days (30-380) (NS). Incremental cost effective analysis showed that plastic stent insertion is the most cost effective option. CONCLUSION: Although all three methods are equally effective in managing an occluded Wallstent, the most cost effective method appears to be plastic stent insertion.

Cholestasis↗
PubMed1998

Specialty group differences over tonsillectomy: pediatricians versus otolaryngologists.

How physicians in different specialties explain their positions on tonsillectomy is explored using data based on in-depth interviews with 53 physicians. Justifications for and against particular indications, assessments of efficacy, and explanations of tonsillar function and pathology are presented. Clear specialty-specific differences exist, especially between pediatricians and otolaryngologists. Opposing specialty views rest upon radically different versions of cost/benefit assessment, whereas evaluations of efficacy are based primarily on conceptual reasoning and anecdotal accounts. Physicians' opinion of clinical trial results are specialty-dependent and are used to sustain specialty viewpoints. The implications of such specialty group differences for public policy are discussed.

Adult↗
PubMed1997

Relationships between the mitochondrial permeability transition and oxidative stress during ara-C toxicity.

The mitochondrial permeability transition and oxidative stress seem to be critical alterations in cellular physiology that take place during programmed cell death. Failure to undergo apoptosis is associated with drug resistance in acute myeloid leukemia and other cancers. Therefore, it is important to establish causal relationships between the physiological changes that take place in apoptosis, because these are potential targets for novel treatment strategies to overcome this form of drug resistance. We describe the use of multilaser flow cytometry methods to make correlated measurements of mitochondrial membrane potential (MMP), the generation of reactive oxygen intermediates, the cellular content of reduced glutathione (GSH), intracellular calcium, and exposure of phosphatidylserine on the cell surface. Using these combined methods, we have mapped a "death sequence" that occurs after treatment of leukemic blasts with clinically relevant concentrations of 1-beta-D-arabinofuranosylcytosine (ara-C). Dual labeling of MMP and cellular glutathione content showed that loss of MMP, indicative of the permeability transition, took place in cells that were depleted of glutathione. The loss of MMP coincided with phosphatidylserine exposure and preceded a state of high reactive oxygen generation. Finally, there was an increase in intracellular calcium. These results demonstrate that the mitochondrial permeability transition takes place during ara-C toxicity but suggest that this occurs downstream of the loss of GSH. Thus, oxidative stress after ara-C-induced toxicity seems to be a biphasic phenomenon, with the permeability transition occurring after a depletion of GSH and preceding a state of high reactive oxygen generation.

Calcium↗
PubMed1997

Disruption of the terminal base pairs of retroviral DNA during integration.

Integrase catalyzes two essential steps in the integration of the retroviral genome--end processing and strand transfer--both of which require the interaction of integrase with viral att sites located at the ends of viral genomic DNA. These two different polynucleotidyl transfer reactions are apparently carried out by a single active site. The end product of these reactions, the integrated provirus, does not undergo transposition and remains a stable part of the host cell genome. A central question in understanding the mechanism of integration is how a single active site accomplishes two distinct polynucleotidyl transfer reactions. We propose that integrase distorts DNA substrates to accommodate both reactions within the active site. Evidence is provided for disruption of base-pairing at the terminus of viral DNA during end processing. Furthermore, we show that this end fraying is a required step in end processing and that it appears to occur after initial binding of the viral DNA end. This requirement for base-pair disruption may account for the inability of integrase to use internal sites on DNA molecules as viral att sites. The specificity of integrase for DNA ends solves a problem posed by the long terminal repeat structure of the viral genome, and may help to prevent transposition of integrated proviruses.

Base Composition↗
PubMed1997

Preoperative chemotherapy versus surgical therapy alone for squamous cell carcinoma of the esophagus: a prospective randomized trial.

OBJECTIVE: This study investigated the role of preoperative chemotherapy in squamous cell cancer of the esophagus. METHODS: A prospective randomized trial was undertaken in 147 patients: 74 received preoperative chemotherapy comprising cisplatin and 5-fluorouracil and 73 had surgical therapy alone. End points were cancer and therapy-related deaths. RESULTS: Sixty-six patients (89%) in the chemotherapy group underwent resection compared with 69 (95%) in the control group (p = not significant). Of the 60 patients who had resection after completing the chemotherapy program, 35 (58%) had a significant response, of whom four (6.7%) had a complete pathologic response. Postoperative mortality rates were 8.3% and 8.7% in the chemotherapy and control groups, respectively (p = not significant). Significant downstaging was evident with chemotherapy; curative resections were possible in 67% of these patients compared with 35% in the control group (p = 0.0003). T3 and T4 tumors were found in 67% and 91% of the chemotherapy and control groups, respectively (p = 0.0002). The respective figures for N1 disease were 70% and 88% (p = 0.009). An intent-to-treat analysis of survival showed no significant difference between the two groups. Median survivals were 16.8 and 13 months, respectively (p = 0.17). Of those who completed the chemotherapy and resection, responders fared better than control patients. Median survivals were 42.2 months and 13.8 months, respectively (p = 0.003). Median survival (8.3 months) was worse for nonresponders than for control patients (p = 0.03). The recurrence pattern suggested a significant reduction in locoregional disease with chemotherapy. CONCLUSIONS: Preoperative chemotherapy was safe and resulted in significant downstaging and an increased likelihood of curative resection. Survival was not better than that in the surgery-alone group, but responders did fare better than nonresponders.

Aged↗
PubMed1997

Successful treatment of post-cholecystectomy bile leaks using nasobiliary tube drainage and sphincterotomy.

OBJECTIVE: Bile leaks are known complications of cholecystectomy. The combination of sphincterotomy and nasobiliary tube (NBT) drainage is effective for the immediate decompression of bile ducts and provides access for follow-up cholangiography. Our objective was to study, retrospectively, 19 patients who had undergone treatment for bile leaks with this combination between October 1991 and December 1995. METHODS: Nineteen patients (15 F, 4 M) ages 23-83 yr (mean 50 yr) presented with bile leaks secondary to open cholecystectomy (n = 1) and laparoscopic cholecystectomy (n = 18). All patients had sphincterotomy and NBT placement. Symptoms, findings at ERCP, and outcome were reviewed. RESULTS: Patients presented from 0 to 150 days after cholecystectomy (median = 2) with pain (n = 17), fever (n = 8), bile leakage in a surgical drain (n = 4), elevated liver tests (n = 8), and nausea and vomiting (n = 4). Fourteen patients had diagnostic imaging before endoscopic management. ERCP findings included cystic stump leak (n = 12), including one with a colocutaneous biliary fistula, gallbladder fossa leak (n = 3), right hepatic branch leak (n = 1), or no leak (n = 3). Three patients had choledocholithiasis. NBT drainage was used for a mean of 3.9 days (range 1-12 days). Fourteen patients had radiographic evidence of leak closure. One patient ultimately required surgical correction for a chronic colocutaneous biliary fistula. There were no early or late endoscopic complications. CONCLUSIONS: Endoscopic management with nasobiliary drainage and sphincterotomy is effective for acute uncomplicated bile leaks but may not be adequate for chronic fistulas. The advantages over endoprostheses include access for subsequent cholangiography, improved biliary decompression, and catheter removal without further endoscopy.

Adult↗
PubMed1996

Flow cytometric calibration of intracellular pH measurements in viable cells using mixtures of weak acids and bases.

We describe a new method for calibrating intracellular pH (pH1) measurements by flow cytometry, based on the null point method proposed originally by Eisner et al. (Pflügers Arch 413:553-558, 1989). The method involves suspending cells loaded with pH-sensitive dyes, such as SNARF-1 or BCECF, in defined mixtures of the weak acid butyric acid and the weak base trimethylamine. Only the uncharged forms of these agents freely permeate the plasma membrane. The weak acid donates protons intracellularly, whereas the weak base accepts them. In accordance with the Henderson-Hasselbalch equation, when cells are exposed to these mixtures, the steady-state pHi is displaced, and the fluorescence signal reflects this new pHi. The null point method described by Eisner et al. derives pHi by determining the molar ratio of acid to base that produces no change in fluorescence signal. In this paper, we show that it is not necessary to obtain the true null point, because a calibration curve can be derived from "pseudo null" values whose pHi is defined by the equation pHi = pHe -0.5 log [(AT)/(BT)], where pHe is the extracellular pH, and (AT) and (BT) are the total concentrations of weak acid and base in the suspension. We refer to this as the "pseudo null calibration method." It is rapid, technically simple, and reproducible. Compared with the widely used nigericin calibration method, it is not influenced by the intracellular potassium concentration; therefore, it may give a more reliable estimate of the absolute value of pHi.

Acid-Base Equilibrium↗
PubMed1996

Bioequivalence of two tablet formulations of nadolol using single and multiple dose data: assessment using stereospecific and nonstereospecific assays.

Nadolol, a nonspecific beta-blocker, is a racemate composed of equal amounts of four stereoisomers, namely, SQ-12148, SQ-12149, SQ-12150, and SQ-12151. In an open-label, randomized, four-period crossover study, the pharmacokinetics of nadolol and its stereoisomers and the bioequivalence of two formulations of nadolol were assessed in 20 healthy male subjects following a single dose (80 mg) and multiple doses (80 mg; once daily for 7 days). A standard granulated tablet and direct compressed tablet formulations, each containing 80 mg of nadolol, with different in vitro dissolution profiles that met current USP requirements were used. The four treatments were single and multiple doses of granulated tablet, and single and multiple doses of compressed tablet. There was a 7 day washout period between successive treatments. All doses of nadolol were administered after an overnight fast. Serial blood samples were collected up to 72 h following the single dose and during multiple dose treatments, following day 6 and 7 doses. Validated high-performance liquid chromatographic assays were applied to measure nadolol and its stereoisomers in the study samples. Plasma concentration data were subjected to noncompartmental pharmacokinetic analysis. Both C(max) and AUC values were significantly greater for SQ-12150 when compared to other nadolol stereoisomers obtained after a single dose or at steady state. However, T(max) and T1/2 values were similar among the four isomers. The observed steady state AUC tau values for nadolol (2278-2331 ng h/ML) or its stereoisomers (550-874 ng h/ML) were significantly greater than those predicted from the single dose AUCinf values (nadolol, 1840-1845 ng h/ML; isomers, 450-713 ng h/ML). The intrasubject variability, computed from multiple dose data, was generally greater for the stereoisomers (17-40%) than for nadolol (10-32%). The two formulations were bioequivalent for nadolol (C(max) = 0.98 [84%, 117%]; AUCinf = 1.03 [93%, 116%]) and SQ-12150 (C(max) = 1.12 [89%, 122%]; AUCinf = 0.98 [82%, 119%]) after a single dose, and only for nadolol (C(max) = 1.07 [84%, 118%]; AUCinf = 1.02 [91%, 113%]) at steady state.

Adult↗