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Biomedical subjects

J W Chow

Publications and source records attributed to J W Chow.

At least 55 records · Page 3Linked to original sources
PubMed1997

The polymerase chain reaction in the diagnosis of early mycosis fungoides.

The earliest or patch stage of mycosis fungoides may present diagnostic difficulty both clinically and pathologically. The present study of the polymerase chain reaction (PCR) as a diagnostic tool in early mycosis fungoides was therefore undertaken, using a rapid PCR method for the detection of gamma- and beta-chain T-cell receptor (TCR) gene rearrangements in routine formalin-fixed, paraffin-embedded histological sections. Forty-two biopsies were studied from 26 patients with mycosis fungoides. Twenty-three skin biopsies with a clinicopathological diagnosis of early, or patch stage, mycosis fungoides were investigated. Of these, 18 (78 per cent) showed TCR-gamma or both beta- and gamma-chain TCR gene rearrangements. TCR gene rearrangements were shown in seven of the 14 plaque stage lesions (50 per cent) and also in the single case of tumour stage disease. Where gene rearrangements were identified, these were identical in all biopsies from an individual patient, irrespective of the site of the lesion, the disease stage, or the time lapse between the biopsies. The PCR is therefore a highly sensitive technique, which can be performed on routine pathological material, in cases where the diagnosis of early mycosis fungoides cannot be made with certainty on conventional histopathological and immunohistochemical grounds.

Adult↗
PubMed1997

Mechanical characteristics of knee extension exercises performed on an isokinetic dynamometer.

The purpose of this study was to evaluate selected mechanical characteristics of knee extension exercises performed on a LIDO Active Isokinetic System. A female subject performed two repetitions of maximal effort knee extension at 16 different preset angular velocities (PAVs). The gravitational and inertial effects were included in the computation of the resultant knee torque. For each repetition, the knee flexion angle, the angular velocity and acceleration of the shank, and the knee torque throughout the range of motion were computed. The shank angular acceleration values indicated that if the inertial effect is not considered the knee torque will be underestimated in the initial phase and errors in knee torque up to about 6 N.m can be expected for the rest of the repetition. The durations when the shank angular velocity was within +/- 5% and +/- 10% of PAV (expressed as percentages of the repetition time) were found to decrease with increasing PAV. The difference between PAV and shank angular velocity at the instant of peak torque also increased with increasing PAV. The results demonstrate the limitations that may exist in an isokinetic dynamometers.

Adult↗
PubMed1997

A novel gentamicin resistance gene in Enterococcus.

Enterococcus gallinarum SF9117 is a veterinary isolate for which the MIC of gentamicin is 256 micrograms/ml. Time-kill studies with a combination of ampicillin plus gentamicin failed to show synergism against SF9117. A probe representing aac(6')-aph(2") did not hybridize to DNA from SF9117. A 3.2-kb fragment from plasmid pYN134 of SF9117 was cloned and conferred resistance to gentamicin in Escherichia coli DH5 alpha. Nucleotide sequence analysis revealed the presence of a 918-bp open reading frame whose deduced amino acid sequence had a region with homology to the C-terminal domain of the bifunctional enzyme AAC(6')-APH(2"). The gene is designated aph(2")-Ic, and its observed phosphotransferase activity is provisionally designated APH(2")-Ic. An intragenic probe hybridized to the genomic DNA from an Enterococcus faecium isolate from the peritoneal fluid of one patient and to the plasmid DNA of an Enterococcus faecalis isolate from the blood of another patient. An enterococcal isolate containing this novel resistance gene might not be readily detected in clinical laboratories that use gentamicin at 500 or 2,000 micrograms/ml for screening for high-level resistance.

Amino Acid Sequence↗
PubMed1996

Estrogen suppresses activation but enhances formation phase of osteogenic response to mechanical stimulation in rat bone.

We used a model whereby mechanical stimulation induces bone formation in rat caudal vertebrae, to test the effect of estrogen on this osteogenic response. Unexpectedly, estrogen administered daily throughout the experiments (8-11 d) suppressed, and ovariectomy enhanced, mechanically induced osteogenesis. Osteogenesis was unaffected by the resorption-inhibitor pamidronate, suggesting that the suppression of bone formation caused by estrogen was not due to suppression of resorption. We found that estrogen did not significantly reduce the proportion of osteocytes that were induced by mechanical stimulation to express c-fos and IGF-I mRNA; and estrogen suppressed mechanically induced osteogenesis whether administration was started 24 h before or 24 h after loading. This suggests that estrogen acts primarily not on the strain-sensing mechanism itself, but on the osteogenic response to signals generated by strain-sensitive cells. We also found that when estrogen administration was started 3 d after mechanical stimulation, by which time osteogenesis is established, estrogen augmented the osteogenic response. This data is consistent with in vitro evidence for estrogen responsiveness in two phenotypically distinct bone cell types: stromal cells, whose functional activities are suppressed, and osteoblasts, which are stimulated, by estrogen.

Animals↗
PubMed1996

Reduction in dynamic indices of cancellous bone formation in rat tail vertebrae after caudal neurectomy.

We have previously noted that a relatively large load (150 N) is required to induce a strain on the cortex of rat vertebrae similar to that induced on weight-bearing bones by normal mechanical usage. It seems unlikely that the musculature of the tail normally imposes loads of this magnitude, and this suggests that the quantity of bone in caudal vertebrae is maintained at a higher level than would be expected for the mechanical environment to which it is exposed. This high bone mass could represent a genetically determined minimum, or could be maintained through increased sensitivity to mechanical stimuli. To distinguish between these two possibilities, we denervated the tails of 13-week-old rats by neurectomy at L6, and assessed the response of the caudal vertebrae to mechanical disuse. We found that caudal neurectomy caused a reduction in the cancellous bone formation rate in the eighth caudal vertebrae to 12% of that seen in sham-operated animals. The cancellous bone formation rate in the thoracic vertebrae of neurectomized rats, which are not mechanically disused by caudal neurectomy, was not significantly reduced. This suggests that the cancellous bone formation rate in vertebrae is maintained by substantially less intense mechanical environments than those prevailing in weight-bearing bones, raising the possibility that bones may differ in their sensitivity to mechanical strain.

Animals↗
PubMed1996

Colitis causes bone loss in rats through suppression of bone formation.

BACKGROUND & AIMS: Idiopathic inflammatory bowel disease (IBD) is associated with bone loss in more than 30% of cases. Nevertheless, the pathogenesis of the bone loss is uncertain. The aim of this study was to investigate the bone loss and underlying mechanisms using an animal model of IBD. METHODS: Severe colitis was induced by intrarectal administration of a hapten, 2,4,6-trinitrobenzenesulfonic acid (TNBS). Severity of IBD was graded macroscopically and histologically. Bone histomorphometry was performed on cancellous bone of the tibiae. RESULTS: A florid transmural colitis was observed 3 weeks after administration of TNBS. In these animals, there was considerable cancellous bone loss of 33% compared with age-matched, pair-fed control animals. This was associated with a marked suppression of the cancellous bone formation rate to < 30% of that in control animals. Thereafter, bone formation rate increased in parallel with healing of colitis. Twelve weeks after TNBS administration, the persistent increase in bone formation rate was associated with return of bone volume to control levels. CONCLUSIONS: The data suggest that bone loss can occur rapidly in colitis and is associated with suppression of bone formation. This study also shows that the bone loss that occurs during TNBS-induced colitis is reversible.

Animals↗
PubMed1996

Bacteremia due to Stenotrophomonas (Xanthomonas) maltophilia: a prospective, multicenter study of 91 episodes.

We identified 91 cases of bacteremia due to Stenotrophomonas (Xanthomonas) maltophilia in a prospective, multicenter observational study. The patients were highly compromised; the majority had an underlying malignancy, had received immunosuppressive therapy, and had indwelling venous catheters. Although 94% of patients received an antimicrobial agent to which the blood isolate was susceptible, the mortality among these patients 14 days after the onset of bacteremia was 21%. Mortality was significantly correlated with the presence of a hematologic malignancy or neutropenia or transplantation, immunosuppressive therapy, and a severity-of-illness score of > 4. S. maltophilia infection is associated with substantial morbidity and mortality among highly compromised patients. The organism is typically resistant to expanded spectrum beta-lactam agents and aminoglycoside antibiotics. Trimethoprim-sulfamethoxazole should be administered if the isolate is susceptible to this combination; addition of another agent to which the isolate is susceptible should be considered in treating patients who are neutropenic, immunocompromised, or critically ill.

Bacteremia↗
PubMed1996

Quantitative comparison in vitro of mutational antibiotic resistance of Enterobacter spp. using a spiral plater.

The presence of spontaneous mutational antibiotic resistance among 18 bacteremic isolates of Enterobacter spp. to cefotaxime, ceftazidime, gentamicin, amikacin, ciprofloxacin, and trimethoprim-sulfamethoxazole was determined quantitatively in vitro using a spiral plater. Each drug was delivered using the device and the agar plates were inoculated in radial streaks. The degree of resistance was estimated by dividing the antimicrobial concentration required to inhibit 90% of the colonies growing in the area beyond the MIC by the MIC itself. The degree of resistance to third-generation cephalosporins and aztreonam was statistically significantly greater than that to co-trimoxazole, imipenem, and ciprofloxacin (P < 0.01); the latter three antibiotics showed virtually no mutational resistance. An intermediate level of resistance was induced by aminoglycosides, and mutational resistance to piperacillin varied between this and the higher levels observed for the cephalosporins. By providing a simple and efficient means of detecting spontaneous mutational resistance, the spiral plater may prove useful in identifying those antimicrobial agents which induce few or no mutants and therefore may be more likely to be successful in treating infections due to Enterobacter spp.

Bacteriological Techniques↗
PubMed1996

Osteocytic expression of mRNA for c-fos and IGF-I: an immediate early gene response to an osteogenic stimulus.

We analyzed the expression, during the osteogenic response of bone to mechanical stimulation, of insulin-like growth factor I (IGF-I), a growth factor implicated in bone formation, and c-fos, a protooncogene in which disordered regulation specifically affects bone. Both genes were strongly expressed in osteocytes of mechanically stimulated but not control bones within 30 min of the osteogenic stimulus. IGF-I mRNA expression increased up to 6 h, was restricted to osteocytes, and was strongly suppressed by indomethacin. Although early IGF-I mRNA expression was resistant to cycloheximide, there was a degree of suppression after 6 h, raising the possibility that IGF-I expression might be prolonged by autocrine mechanisms. c-fos mRNA was increased both in osteocytes and on bone surfaces. At both sites, c-fos expression was transient, prolonged by cycloheximide, and was strongly stimulated even in the presence of indomethacin. Thus osteocytes respond to mechanical stimulation with immediate prolonged expression of IGF-I and immediate transient expression of c-fos, implicating osteocytes in the osteogenic response to mechanical stimulation. Moreover, the different spatial distribution and indomethacin sensitivity of c-fos and IGF-I gene expression suggest that at least two signaling pathways are activated in osteocytes during this process.

Animals↗
PubMed1996

Nitric oxide is an early mediator of the increase in bone formation by mechanical stimulation.

We tested the ability of NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthase (NOS), to suppress the osteogenic response in a recently developed model of mechanically induced osteogenesis. L-NMMA was given either as a single intraperitoneal dose, 15 min before the episode of mechanical stimulation, or as four doses every 6 h, commencing 2 h after loading. Administration of L-NMMA before loading completely prevented the increase in cancellous bone formation by mechanical stimulation. This suppression was largely lost when L-NMMA was administered after loading. Thus the response is likely to be due to activation of a preexistent constitutive NOS in bone cells during or very soon after mechanical stimulation. Suppression of the osteogenic response by L-NMMA was prevented by coadministration of L-arginine but not by the inactive isomer, D-arginine. These changes in cancellous bone were mirrored by similar changes on the corticoendosteal and periosteal bone surfaces. These data suggest that early release of NO is a key signal in the transduction of mechanical stimuli into subsequent bone formation.

Animals↗
PubMed1995

Sequential analysis of gene expression after an osteogenic stimulus: c-fos expression is induced in osteocytes.

We have recently developed an experimental model whereby mechanical stimulation induces osteogenesis in the caudal vertebrae of rats. We used this model to assess expression of genes induced by mechanical loading. Bulk preparations of mRNA extracted after loading did not show > 2-fold increases in expression of mRNA for matrix proteins or growth factors in Northern blotting analysis. c-jun was undectable. However, c-fos showed a 4-fold increase in expression within 60 mins of loading, before returning to control levels by 4 hrs. This increase was associated with intense signals in in situ hybridization, not seen in any nonloaded vertebrae, for c-fos over cortical osteocytes: thus osteocytes respond to mechanical loading with c-fos expression so strongly as to be visible even in the bulk RNA preparations. The results represent persuasive evidence for a role for osteocytes, and for c-fos, in the osteogenic response of bone to mechanical stimulation.

Animals↗
PubMed1995

Stimulation of bone formation by dynamic mechanical loading of rat caudal vertebrae is not suppressed by 3-amino-1-hydroxypropylidene-1-bisphosphonate (AHPrBP).

We have recently developed an experimental system whereby pins inserted into the seventh and ninth caudal vertebrae of rat tails are used to load the eighth caudal vertebrae (C-8) in compression. In this model, a single 5-min period of dynamic loading, sufficient to induce strains within the range to which bones are exposed under physiological circumstances, stimulates lamellar bone formation in the cancellous bone of the vertebrae. The rapidity with which the increase in bone formation was induced raised the possibility that this bone formation might have occurred without prior resorption. To test the role of bone resorption in the response of the bone to mechanical stimulation, we compared the anabolic response to a single period of loading, of rats treated with 3-amino-1-hydroxypropylidene-1-bisphosphonate (AHPrBP) or vehicle. We found that mechanical loading caused a significant increase in dynamic and static indices of bone formation. The same indices were unaffected by AHPrBP, while the bone formation rate in the tibiae was reduced by AHPrBP. These results suggest that the increased bone formation induced by mechanical stimulation in the cancellous bone of rat vertebrae is not dependent on bone resorption.

Animals↗
PubMed1995

An outbreak of infusion-related Klebsiella pneumoniae bacteremia in a liver transplantation unit.

Over a 1-month period, there were five episodes of infusion-related Klebsiella pneumoniae bacteremia in four liver transplantation patients housed in the same ward. Investigation of nursing practices revealed that a common normal-saline bag, to which intravenous (iv) tubing and a stopcock were attached, was used to flush iv catheters. The iv tubing and stopcock were changed at sporadic intervals. Cultures of the normal saline and iv equipment yielded K. pneumoniae, which had the same susceptibility pattern as the patients' isolates. Isolates recovered during the outbreak from the patients and from the iv saline/equipment were of the same strain, as determined by pulsed-field electrophoresis of Xba I-digested genomic DNA. Termination of the practice of flushing iv catheters with a common normal-saline bag halted the outbreak.

Adult↗
PubMed1995

Characterization of antimicrobial resistance in enterococci of animal origin.

Among 97 enterococci cultured from animals, gentamicin MICs were > or = 2,000 micrograms/ml for 9 isolates and between 250 and 1,024 micrograms/ml for 6 isolates. For two isolates tested (gentamicin MICs, 256 and 512 micrograms/ml, respectively), there was no in vitro synergy with penicillin plus gentamicin, resistance was transferable, and there was no hybridization with a probe specific for 6'-aminoglycoside acetyltransferase-2"-aminoglycoside phosphotransferase. The results of the study indicate the presence of a unique gentamicin resistance genotype in enterococci of animal origin.

Animals↗
PubMed1995

DNA hybridization and contour-clamped homogeneous electric field electrophoresis for identification of enterococci to the species level.

In this study, 113 Enterococcus faecium, 37 Enterococcus faecalis, 24 Enterococcus gallinarum, 15 Enterococcus raffinosus, and 13 Enterococcus casseliflavus clinical isolates and American Type Culture Collection (ATCC) strains were evaluated by contour-clamped homogeneous electric field electrophoresis. Thirty-one of the E. faecium, 22 of the E. faecalis, 24 of the E. gallinarum, 15 of the E. raffinosus, and 13 of the E. casseliflavus isolates were also evaluated by DNA-DNA hybridization. Genomic DNAs from type strains E. faecalis ATCC 19433, E. faecium ATCC 19434, E. gallinarum ATCC 49573, E. raffinosus ATCC 49427, and E. casseliflavus ATCC 25788 were labeled with biotin for use as probes. E. faecalis differed from all other species in always having a largest fragment of > 400 kb. E. gallinarum was different from all other species in having all SmaI fragments of < 200 kb. Biotin-labeled probes showed a high degree of hybridization with genomic DNA from the same species and a low degree of hybridization when hybridized to genomic DNA from different species for all isolates tested except for four isolates identified as E. faecium by conventional biochemical methods. The DNA from these four isolates hybridized strongly to DNA from E. gallinarum ATCC 49573 and weakly to E. faecium ATCC 19434 DNA and had all SmaI fragments of < 200 kb in size. These data suggest that these isolates are nonmotile E. gallinarum. DNA from each ATCC type strain hybridized strongly with itself and had only a low degree of hybridization with DNA from other ATCC type strains tested. These results suggest that contour-clamped homogeneous electric field electrophoresis patterns and DNA-DNA hybridization with biotin-labeled probes may be of use for species differentiation of some enterococci.

Blotting, Southern↗