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Biomedical subjects

C Cheng

Publications and source records attributed to C Cheng.

At least 163 records · Page 9Linked to original sources
PubMed1992

The development of synthetic polymers that resist encrustation on exposure to urine.

The consequences of long-term exposure of synthetic materials to urine have prevented the development of alloplastic replacement of diseased or damaged parts of the urinary tract. Similarly, urethral and ureteric catheters require regular replacement if the complications of encrustation and blockage are to be avoided. The mechanism of encrustation is not understood completely and thus it is unclear why certain materials appear better able to resist encrustation. This study has involved the development of a new encrustation model to provide a reproducible and quantitative assessment of the susceptibility of polymers to encrustation. This model will allow beneficial characteristics of co-polymer design to be recognised, with the aim of finding new materials that are tolerant of exposure to urine. Results of co-polymers examined show that the incorporation of fluorine-containing components confers significant resistance to the formation of encrustation. It is suggested that the physico-chemical properties of polymer surfaces may be important determinants of resistance to encrustation.

Calcium↗
PubMed1992

Identification of hepatitis C viruses with a nonconserved sequence of the 5' untranslated region.

The nucleotide sequence of the 5' untranslated region of hepatitis C virus (HCV) has been shown to be conserved. In contrast, we have detected more sequence variation in this region in several HCV isolates than hitherto expected. The nucleotide sequences of the 5' untranslated regions of these isolates differ significantly from that of the prototype but are very similar to each other. We believe that these isolates belong to the same type of HCV. Among 240 HCV RNA polymerase chain reaction-positive specimens that we examined, 7 belong to this type. The results suggest that the HCV variants that we detected represent a different type of HCV and that they are responsible for approximately 3% of HCV infections in patients that we have examined.

Base Sequence↗
PubMed1992

Laparoscopic nephrectomy in a porcine model.

Laparoscopic nephrectomy was performed in 15 male pigs, the procedure was successful in 14. Extraction of the intact kidney through a 5-cm lower abdomen incision was done in 7 animals; complete destruction and evacuation of the kidney was accomplished by a round-knife suction device through a 1-cm port in another 7 pigs. Grossly, the specimen consisted of sausage-like tubular renal tissue and a small amount of tissue debris. Pathology revealed that the glomerular and tubular structures were well preserved, no interstitial hematoma could be found. Four ports were usually used, one 1-cm umbilical camera port, one 0.5-cm port for ureter traction, and two 1-cm working ports along the midclavicular line. All the pigs recovered uneventfully. The average operation time was 3 h 20 min. The application of endo-GIA (United States Surgical Corporation) for renal hilum reduced the operative time to 2 h 20 min. Complications included renal vein tear during endoclip application and cutting in the first case, mild subcutaneous emphysema in 2 cases. This first pig received exploratory laparotomy for the repair and ligation of the renal vein. No more major complications occurred with increasing experience. From this porcine experiment, we conclude that the combination of laparoscopy, a tissue destroyer and an endobag for the entrapment of kidney seem to be a promising technique for clinical nephrectomy.

Animals↗
PubMed1992

Management of severe chronic radiation cystitis.

Chronic radiation cystitis complicating pelvic irradiation can occasionally result in massive bleeding difficult to control with conventional means. Between 1986 and 1989, we managed 42 cases of chronic radiation cystitis of which nine (21%) were of this severe type based on the necessity for repeated cystodiathermy, massive transfusions and open surgical intervention. We found early cystodiathermy and alum bladder irrigation beneficial in early cases, but six (67%) patients required emergency bilateral percutaneous nephrostomies for proximal urinary diversions to help stop the bleeding. Despite aggressive treatment, two patients (22%) died during their admissions and two others (22%) died shortly after discharge. Three patients eventually required elective ileal conduit diversion for their contracted defunctioned bladder. Thus this group of patients suffered relatively high morbidity and mortality for an essentially benign condition. Increased physician awareness and timely percutaneous nephrostomies may improve results.

Aged↗
PubMed1991

Dexamethasone prevents the growth inhibitory effects of recombinant tumor necrosis factor in a rat hepatoma cell line Reuber-RC-3: an association with the changes in the messenger RNA levels for multidrug resistance gene.

Two days exposure to recombinant tumor necrosis factor (rTNF-alpha) produced a dose-dependent reduction in (methyl-3H) thymidine incorporation in RC-3 cells (ID50 = 25 units/ml). Prolonged treatment with rTNF-alpha further resulted in a significant reduction in colony formation (ID50 = 200 units/ml), which was reversed upon removal of the agent. Interferon levels were undetectable in the supernatants of the rTNF-alpha treated cells. Simultaneous exposure to dexamethasone prevented the growth inhibition in rTNF-alpha-treated RC-3 cells. Significant dose-dependent increase in the steady state levels of the mRNA for multidrug resistance (MDR1) gene was observed after rTNF-alpha treatment while simultaneous exposure to dexamethasone produced a substantial reduction in the mRNA levels for MDR1 gene. These data suggest that growth inhibitory effects of TNF are regulated by dexamethasone and are associated with changes in MDR1 mRNA levels in hepatoma-derived cells.

Animals↗
PubMed1991

Detubularisation in cystoplasty: clinical review.

Cystoplasty using a detubularised bowel segment is preferable to using a tubularised length of intestine. This has been shown experimentally to result in a reduction in the contractility of the neobladder, although contractions are not completely abolished. Incontinence, especially nocturnal, may still be a problem. Assessment of renal function has shown a marked incidence of upper tract dysfunction despite detubularisation. All patients remain at risk of upper tract obstruction following cystoplasty. Because bowel contraction waves are brought on by distension, it may be possible either to postpone or to prevent the onset of contractions by avoiding an excessive build-up of bladder volume. Clean intermittent self-catheterisation is an efficient means of emptying the bladder, although sphincter rebalancing may also be required.

Adult↗
PubMed1991

Alterations in epidermal biochemistry as a consequence of stage-specific genetic changes in skin carcinogenesis.

The induction of cancer on mouse skin by initiation-promotion protocols occurs through stages in which a benign squamous papilloma is an obligate precursor of squamous cell carcinoma. Activation of the Ha-ras gene is sufficient to produce the papilloma phenotype, while additional genetic changes are required for malignant conversion. The introduction of Ha-ras into normal keratinocytes suppresses the expression of differentiation markers, keratin K1 and K10, and loricrin (a cornified envelope precursor) and, to a lesser extent, filaggrin, at the level of transcription. However, cells initiated by Ha-ras express a nonepidermal keratin, K8. The transcription of K8 in these cells is sensitive to the level of medium Ca2+, being abundant in 0.5 mM Ca2+ and not detected in 0.05 mM Ca2+. Epidermal differentiation is regulated by signalling, which involves changes in phosphatidylinositol turnover and intracellular Ca2+. Cells initiated by Ha-ras do not differ from normal keratinocytes in their intracellular Ca2+ response patterns, at least in response to changes in extracellular Ca2+ and serum factors. However, c-Ha-ra keratinocytes have a high basal level of phosphatidylinositol (PI) turnover, which is additive with several other inducers of this pathway, including Ca2+ and aluminum fluoride. Additional studies suggest that high turnover of the PI pathway is incompatible with differentiation-specific gene expression in keratinocytes. We suggest this negative relationship is mediated through elevated diacylglycerol production and chronic down-modulation of protein kinase C. Protein kinase C is known to be essential for expression of differentiation-related genes in keratinocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Efficient production of Taka-amylase A by Trichoderma viride.

An efficient heterologous protein production system was developed in Trichoderma viride, a very efficient cellulase producer. An expression vector containing the Taka-amylase A gene from Aspergillus oryzae, which was fused to the strong promoter and signal peptide sequence of the cellobiohydrolase 1 gene (cbh1) of T. viride, and the hygromycin B resistance gene was used to transform protoplasts of T. viride. Using hygromycin B resistance, a frequency of 3 transformants per microgram DNA on average was obtained. One transformant showed highly elevated alpha-amylase production, 1.0 g/l, which was shown to be under the control of the cbh1 gene promoter. Analysis of the chromosomal DNA of the transformant showed the integration of more than one copy of the vector.

Base Sequence↗
PubMed1990

Identification of a major keratinocyte cell envelope protein, loricrin.

During epidermal cell cornification, the deposition of a layer of covalently cross-linked protein on the cytoplasmic face of the plasma membrane forms the cell envelope. We have isolated and characterized cDNA clones encoding a major differentiation product of mouse epidermal cells, which has an amino acid composition similar to that of purified cell envelopes. Transcripts of this gene are restricted to the granular layer and are as abundant as the differentiation-specific keratins, K1 and K10. An antiserum against a C-terminal peptide localizes this protein in discrete granules in the stratum granulosum and subsequently at the periphery of stratum corneum cells. Immunofluorescence and immunoelectron microscopy detect this epitope only on the inner surface of purified cell envelopes. Taken together, these results suggest that it is a major component of cell envelopes. On the basis of its presumed function, this protein is named loricrin.

Amino Acid Sequence↗
PubMed1990

The v-ras oncogene inhibits the expression of differentiation markers and facilitates expression of cytokeratins 8 and 18 in mouse keratinocytes.

Cultured mouse keratinocytes can be initiated in vitro by the introduction of a v-rasHa gene by viral transduction. Previous studies indicated that v-rasHa-transduced keratinocytes have a high proliferation rate in medium with 0.05 mM Ca2+ and resist terminal differentiation in medium with greater than 0.1 mM Ca2+, a culture condition in which normal cells mature into squames. The current studies demonstrate that v-rasHa keratinocytes do not express transcripts or protein for epidermal early differentiation markers keratins 1 and 10 when cells are challenged with 0.12 mM Ca2+, which is a signal for expression of these genes in normal cells. Both transcript and protein for the late differentiation marker loricrin are also diminished in v-ras keratinocytes, but filaggrin, also a late differentiation-related gene product, is expressed in nearly normal amounts but at a different Ca2+ optimum. Modification of intracellular Ca2+ with ionomycin failed to restore the expression of any suprabasal keratinocyte markers. In contrast to the effects on normal products of keratinocyte differentiation, the introduction of the v-rasHa gene facilitated the expression of keratins 8 (K8) and 18 (K18). These keratins are characteristic of embryonic cells and cells of simple adult epithelia but not stratified squamous epithelia such as skin. Like normal differentiation markers, the expression of K8 and K18 was dependent both on the v-ras oncogene and the Ca2+ concentration of the culture medium, with greater than 0.1 mM Ca2+ being optimal. At the optimal Ca2+ level, the majority of v-ras keratinocytes expressed K8 and K18 after 96 h, and many cells had reduced amounts of the normal keratinocyte cytokeratin K14. These studies indicate that the v-ras gene causes substantial reprogramming of epidermal physiology, producing an unusual phenotype devoid of early suprabasal markers but at least partially permissive for late marker expression. Furthermore, the Ca2(+)-dependent expression of K8 and K18 suggests that a normal signalling pathway used in keratinocyte differentiation is diverted to an abnormal endpoint.

Animals↗
PubMed1990

Response of Haemophilus somnus to iron limitation: expression and identification of a bovine-specific transferrin receptor.

Nine clinical isolates of Haemophilus somnus were screened for their ability to use different transferrins as a source of iron growth. All nine strains were capable of using bovine but not porcine, human or chicken transferrin. A screening assay for siderophore production did not show any evidence of siderophore production by these strains. When iron-deficient cells from these strains were screened for their ability to bind peroxidase-conjugated transferrin, binding was detected with conjugated bovine, but not human or porcine transferrin. Competition binding studies demonstrated that the binding of peroxidase-conjugated bovine transferrin was competitively inhibited by unconjugated bovine transferrin but not transferrin from other species. The induction of receptor expression by low iron conditions was inhibited by chloramphenicol and rifampicin but not ampicillin indicating that new protein and mRNA synthesis was required for expression of receptor activity. Affinity isolation of receptor proteins with biotinylated bovine transferrin, but not human or porcine transferrin, yielded three proteins from H. somnus strain H74. Two of the proteins were identified as 105 kDa and 73 kDa iron-regulated outer membrane proteins. A third protein of 85 kDa that was isolated did not co-migrate with any iron-regulated outer membrane protein. Affinity isolation of receptor proteins from other strains of H. somnus yielded a 73 kDa protein from all strains and a 105 kDa and 85 kDa protein in four of the six strains analysed.

Animals↗
PubMed1990

Cystoplasty: tubularisation or detubularisation?

Previous studies on substitution or augmentation cystoplasty have highlighted the profusion of surgical techniques available, but there is disagreement as to which is the best. We established an animal model to compare various types of cystoplasties, tubularised and detubularised, using ileum and caecum. Detubularisation did not abolish intrinsic bowel contractions but delayed their onset. No differences were noted in the frequency and amplitude of such contractions after detubularisation or between large and small bowel cystoplasties. Although intravenous urography did not demonstrate any abnormality in upper tract anatomy, a significant number of animals had some functional disturbance of the kidney after cystoplasty demonstrable on isotope renography, irrespective of the surgical technique. It may be possible to prevent these contractions with their associated harmful effects by preventing the bladder volume from building up excessively.

Animals↗