Biomedical subjects

C Cheng

Publications and source records attributed to C Cheng.

At least 109 records · Page 6Linked to original sources

PubMed1998

Cryptococcal prostatic abscess in an immunocompromised patient: a case report and review of the literature.

A case of cryptococcal prostatic abscess in a 65-year-old Chinese man with immunosuppression from treatment of myasthenia gravis is presented. The patient was diagnosed to have cryptococcaemia when he presented with fever and urinary symptoms. Further investigations confirmed cryptococcal meningitis and imaging studies showed a hypodense lesion in the prostate. This proved to be an abscess and it was deroofed transurethrally. Histology of the prostatic tissue revealed the presence of Cryptococcus. The prostate can be a site of persistent cryptococcal infection and may take the form of an abscess. It should be drained transurethrally to prevent relapse.

Abscess↗

PubMed1998

Studies on chemical constituents and immunological function activity of hairy root of Astragalus membranaceus.

Using a large-scale culture technique, the hairy roots of Astragalus membranaceus were produced with a yield reaching 10 g/L. The results from RP-HPLC detection showed that the contents of crude saponin and astragaloside i.v. in the hairy roots were 5.81% and 0.14%, respectively. Six isoflavonoid compounds were also determined. Polysaccharide analysis showed that the total polysaccharide content in the hairy roots was 22.97%; of this content, acidic 8.29% and soluble 14.88%. In comparison with the dry roots, the hairy roots contained higher crude saponin and soluble polysaccharide contents, similar astragaloside i.v. content and lower contents of 6 isoflavonoids, total and acidic polysaccharides, showing that the quality of both types of roots was similar. Regaining the immunity function of rats with low immunity after feeding the aqueous extract of the hairy roots produced by large-scale culture showed that its capacity was similar to the dry roots of A. membranaceus in increasing the immunity function. The results in this paper give evidence that the hairy roots may be a new source of A. membranaceus.

Animals↗

PubMed1998

Outcome of obstructive uropathy after pelvic irradiation in patients with carcinoma of the uterine cervix.

The natural history and outcome of intervention for obstructive uropathy were studied retrospectively in 20 patients managed at the Department of Urology, Singapore General Hospital between 1991 and 1997. The diagnoses of these strictures were made between 10 months and 21 years after the initial treatment. There were 9 (45%) malignant and 11 (55%) benign strictures. The site of ureteric obstruction was in the lower ureter in 15 patients, in the middle ureter in 3 patients and in the upper ureter in 2 patients. Comparisons between malignant and benign strictures showed that patients with higher original stage of tumour were more likely to have malignant strictures. Besides latency period between primary treatment of the tumour and diagnosis of uropathy, bilaterality and site of strictures showed no discernible difference between benign and malignant strictures. Ureteric stenting provided good outcome in 5 patients with benign strictures and in 3 patients with malignant strictures. Open surgical reconstruction was performed on 2 patients with benign strictures and 2 patients with malignant strictures. All these four patients showed good outcome. Ureteric stenting is an acceptable treatment of benign ureteric stricture and for selected patients with malignant strictures. Open surgery is recommended in patients with benign strictures who could not be treated successfully on stenting.

Cystitis↗

PubMed1998

A case report--delayed vesicocutaneous fistula after radiation therapy for advanced vulvar cancer.

This is the first case report of a vesicocutaneous fistula related to prior radiation therapy for recurrent vulvar cancer. Urinary tract complications happen not infrequently after radiation therapy for various pelvic malignancy. It can occur as long as 30 years after cessation of such therapy. Urinary incontinence or obstructive uropathy is, by far, the most common complication. The authors report an unusual complication secondary to radiation therapy. The aetiology, presentation and management of this patient were discussed.

Aged↗

PubMed1998

Knowledge-based visualization of time-oriented clinical data.

We describe a domain-independent framework (KNAVE) specific to the task of interpretation, summarization, visualization, explanation, and interactive exploration in a context-sensitive manner through time-oriented raw clinical data and the multiple levels of higher-level, interval-based concepts that can be abstracted from these data. The KNAVE exploration operators, which are independent of any particular clinical domain, access a knowledge base of temporal properties of measured data and interventions that is specific to the clinical domain. Thus, domain-specific knowledge underlies the domain-independent semantics of the interpretation, visualization, and exploration processes. Initial evaluation of the KNAVE prototype by a small number of users with variable clinical and informatics training has been encouraging.

Artificial Intelligence↗

PubMed1997

Targeted disruption of the epidermal growth factor receptor impairs growth of squamous papillomas expressing the v-ras(Ha) oncogene but does not block in vitro keratinocyte responses to oncogenic ras.

We have assessed the role of epidermal growth factor receptor (EGFR) signaling in biological responses to the v-ras(Ha) oncogene using primary keratinocytes from Egfr -/- mice and wild-type littermates. On the basis of several criteria, Egfr -/- keratinocytes were unresponsive to either acute or chronic exposure to several EGFR ligands but were stimulated to proliferate in response to several other mitogens. Although conditioned medium from primary keratinocytes transduced with v-ras(Ha) retrovirus (v-ras(Ha) keratinocytes) was a potent mitogen for wild-type but not Egfr -/- keratinocytes, v-ras(Ha) transduction of primary keratinocytes of either genotype resulted in a strong mitogenic response, arguing against an obligatory role for EGFR activation in v-ras(Ha)-mediated stimulation of keratinocyte proliferation. Infection with high-titer v-ras(Ha) retrovirus altered the keratin expression pattern in keratinocytes of both genotypes, suppressing differentiation-specific keratins K1 and K10 while activating aberrant expression of K8 and K18. In wild-type but not Egfr -/- cultures, K1 and K10 were also suppressed following infection at lower retroviral titers, presumably as a result of paracrine EGFR activation on uninfected cells present in these cultures. Squamous papillomas produced by grafting Egfr -/- v-ras(Ha) keratinocytes onto nude mice were only 21% of the size of wild-type v-ras(Ha) tumors, and a striking redistribution of S-phase cells was detected by immunostaining for bromodeoxyuridine. In Egfr -/- v-ras(Ha) papillomas, the fraction of total labeled nuclei detected in suprabasal layers was increased from 19 to 39%. In contrast, the basal layer labeling index of Egfr -/- papillomas was reduced to 34%, compared to 43% in wild-type tumors. Our results indicate that, although autocrine EGFR signaling is not required for keratinocyte responses to oncogenic ras in culture or benign tumor formation in nude mouse grafts, disruption of this pathway impairs growth of v-ras(Ha) papillomas by a mechanism that may involve alterations in keratinocyte cell cycle progression and/or migration in vivo.

Animals↗

PubMed1997

Near nerve local insulin prevents conduction slowing in experimental diabetes.

Insulin may have direct effects on axons through its actions on insulin receptors or through cross occupancy of insulin-like growth factor-1 receptors. We tested the hypothesis that insulin itself influences conduction of myelinated fibers independent of hyperglycemia in experimental diabetes. Low dose intermittent (0.2 units thrice weekly) Toronto (regular) insulin was injected at the sciatic notch and knee near the left sciatic nerve of rats rendered diabetic with citrate buffered streptozotocin or nondiabetic rats given citrate only. Identical volumes of normal saline were injected near the contralateral right sciatic nerve. The diabetic rats developed hyperglycemia, elevated glycosylated hemoglobin levels and had slowing of right (saline treated) sciatic tibial motor and caudal sensory conduction velocity. In contrast, local insulin treatment on the left side prevented conduction slowing, unilaterally increasing conduction velocity. In nondiabetic rats, conduction velocities were slightly higher on the insulin treated side, but the influence of insulin was less robust than in diabetics. The insulin treated sural branches of the sciatic nerves in diabetics had a higher percentage of small (< or = 9.0 microm diameter) myelinated fibers than the saline treated nerves. Local insulin has a trophic influence on myelinated fibers that is prominent in diabetic nerves and is independent of hyperglycemia.

Animals↗

PubMed1997

Lignans and isoflavonoids in plasma and prostatic fluid in men: samples from Portugal, Hong Kong, and the United Kingdom.

BACKGROUND: Chinese men have lower incidences of prostate cancer compared to men from Europe and North America. Asians consume large quantities of soya, a rich source of isoflavanoids phyto-oestrogens and have high plasma and urinary levels of these compounds. The mammalian lignans, enterolactone and enterodiol, are another group of weak plant oestrogens and are derived from seeds, cereals and grains. Vegetarians have high plasma and urinary concentrations of lignans. METHODS: The concentrations lignans and isoflavonic phyto-oestrogens were determined by gas chromatography-mass spectrometry (GC-MS) in plasma and prostatic fluid from Portuguese, Chinese and British men consuming their traditional diets. RESULTS: In prostatic fluid the mean concentrations of enterolactone were 31, 162 and 20.3 ng/ml for Hong Kong, Portugal and Britain respectively. Very high levels of enterolactone (> 600 ng/ml) were observed in the prostatic fluid of some of the men from Portugal. High concentrations of equol (3270 ng/ml) and daidzein (532 ng/ml) were found in a sample of prostatic fluid from Hong Kong. Higher mean levels of daidzein were observed in prostatic fluid from Hong Kong at 70 ng/ml, compared to 4.6 and 11.3 ng/ml in samples from Portugal and Britain respectively. Mean levels of daidzein were higher in the plasma samples from Hong Kong (31.3 ng/ml) compared to those from Portugal (1.3 ng/ml) and Britain (8.2 ng/ml). In general, the mean plasma concentrations of enterolactone from the three centres were similar, at 6.2, 3.9 and 3.9 ng/ml in samples from Hong Kong Portugal and Britain respectively. CONCLUSIONS: Higher concentrations of the isoflavanoid phyto-oestrogens, daidzein and equol, were found in the plasma and prostatic fluid of men from Hong Kong compared to those from Britain and Portugal. However, the levels of the lignan, enterolactone, were very much higher in prostatic fluid of Portuguese men. Isoflavanoids and lignans have many interesting properties and may, in part, be responsible for lower incidences of prostate cancer in men from Asia and also some Mediterranean countries. The isoflavanoids from soya, which are present in high concentrations in the prostatic fluid of Asian men, may be protective against prostate disease.

4-Butyrolactone↗

PubMed1997

Kinetic analysis of DNA and RNA strand transfer reactions catalyzed by vaccinia topoisomerase.

Vaccinia topoisomerase binds duplex DNA and forms a covalent DNA-(3'-phosphotyrosyl) protein adduct at the sequence 5'-CCCTT downward arrow. The enzyme reacts readily with a 36-mer CCCTT strand (DNA-p-RNA) composed of DNA 5' and RNA 3' of the scissile bond. However, a 36-mer composed of RNA 5' and DNA 3' of the scissile phosphate (RNA-p-DNA) is a poor substrate for covalent adduct formation. Vaccinia topoisomerase efficiently transfers covalently held CCCTT-containing DNA to 5'-OH-terminated RNA acceptors; the topoisomerase can therefore be used to tag the 5' end of RNA in vitro. Religation of the covalently bound CCCTT-containing DNA strand to a 5'-OH-terminated DNA acceptor is efficient and rapid (krel > 0.5 s-1), provided that the acceptor DNA is capable of base pairing to the noncleaved DNA strand of the topoisomerase-DNA donor complex. The rate of strand transfer to DNA is not detectably affected by base mismatches at the 5' nucleotide of the acceptor strand. Nucleotide deletions and insertions at the 5' end of the acceptor slow the rate of religation; the observed hierarchy of reaction rates is as follows: +1 insertion > -1 deletion > +2 insertion >> -2 deletion. These findings underscore the importance of a properly positioned 5'-OH terminus in transesterification reaction chemistry, but they also raise the possibility that topoisomerase may generate mutations by sealing DNA molecules with mispaired or unpaired ends.

Catalysis↗

PubMed1997

Inhibition of nitric oxide synthase enhances peripheral nerve regeneration in mice.

We tested the hypothesis that inhibition of nitric oxide synthase (NOS) following transection of the sciatic nerve in the mouse would adversely influence regeneration of myelinated fibers from the proximal stump. NOS was inhibited by N(omega)-nitro-L-arginine-methyl ester (L-NAME; 10 mg/kg i.p.), a broad spectrum NOS inhibitor given twice daily for the first 10 days following nerve transection in Swiss mice. Controls received the inactive enantiomer N(omega)-nitro-D-arginine methyl ester (D-NAME). Regeneration was assessed by serial recordings of the M potential from interosseous muscles of the foot innervated by sciatic-tibial motor fibers and morphometric analysis of myelinated fibers distal to the injury site. Contrary to expectation, M potentials reappeared earlier in the mice treated with L-NAME and were higher in amplitude (reflecting the number of reinnervating motor fibers) at 10 weeks after the injury. In the L-NAME treated mice, the mean axonal diameter of regenerating tibial myelinated fibers was larger and the fiber size histogram was shifted to larger fibers. Inhibition of NOS in a transected peripheral nerve is associated with enhanced regeneration of myelinated fibers. Local elaboration of NO may be toxic to regenerating axons.

Animals↗

PubMed1997

Characterization of an ATP-dependent DNA ligase encoded by Haemophilus influenzae.

We report that Haemophilus influenzae encodes a 268 amino acid ATP-dependent DNA ligase. The specificity of Haemophilus DNA ligase was investigated using recombinant protein produced in Escherichia coli. The enzyme catalyzed efficient strand joining on a singly nicked DNA in the presence of magnesium and ATP (Km = 0.2 microM). Other nucleoside triphosphates or deoxynucleoside triphosphates could not substitute for ATP. Haemophilus ligase reacted with ATP in the absence of DNA substrate to form a covalent ligase-adenylate intermediate. This nucleotidyl transferase reaction required a divalent cation and was specific for ATP. The Haemophilus enzyme is the first example of an ATP-dependent DNA ligase encoded by a eubacterial genome. It is also the smallest member of the covalent nucleotidyl transferase superfamily, which includes the bacteriophage and eukaryotic ATP-dependent polynucleotide ligases and the GTP-dependent RNA capping enzymes.

Adenine↗

PubMed1997

Mutational analysis of 39 residues of vaccinia DNA topoisomerase identifies Lys-220, Arg-223, and Asn-228 as important for covalent catalysis.

Vaccinia DNA topoisomerase, a 314-amino acid type I enzyme, catalyzes the cleavage and rejoining of DNA strands through a DNA-(3'-phosphotyrosyl)-enzyme intermediate. To identify amino acids that participate in the transesterification reaction, we introduced alanine substitutions at 39 positions within a conserved 57amino acid segment upstream of the active-site tyrosine. Purified wild type and mutant proteins were compared with respect to their activities in relaxing supercoiled DNA. The majority of mutant proteins displayed wild type topoisomerase activity. Mutant enzymes that relaxed DNA at reduced rates were subjected to kinetic analysis of the strand cleavage and religation steps under single-turnover and equilibrium conditions. For the wild type topoisomerase, the observed single-turnover cleavage rate constant (kcl) was 0.29 s-1 and the cleavage-religation equilibrium constant (Kcl) was 0.22. The most dramatic mutational effects were seen with R223A; removal of the basic side chain reduced the rates of cleavage and religation by factors of 10(-4.3) and 10(-5.0), respectively, and shifted the cleavage-religation equilibrium in favor of the covalently bound state (Kcl = 1). Introduction of lysine at position 223 restored the rate of cleavage to 1/10 that of the wild type enzyme. We conclude that a basic residue is essential for covalent catalysis and suggest that Arg-223 is a constituent of the active site. Modest mutational effects were observed at two other positions (Lys-220 and Asn-228), at which alanine substitutions slowed the rates of strand cleavage by 1 order of magnitude and shifted the equilibrium toward the noncovalently bound state. Arg-223 and Lys-220 are conserved in all members of the eukaryotic type I topoisomerase family; Asn-228 is conserved among the poxvirus enzymes.

Amino Acid Sequence↗

PubMed1997

Measurement and metabolism of isoflavonoids and lignans in the human male.

Asian men, who consume a low fat/high fibre soya-based diet, have very much lower incidence of prostate cancer than men from North America and Europe. The soya bean is a rich source of the isoflavonic phyto-oestrogens, daidzein, genistein and equol, compounds which may be cancer-protective in Asian populations. The lignans, enterolactone and enterodiol, plant oestrogens derived from cereals and vegetables, may act in a similar manner in vegetarian men. We report here on the measurement of isoflavonoids and lignans, by gas chromatography-mass spectrometry, in prostatic fluid of men from Asia and Europe and also on the metabolism of these compounds in Western men following dietary supplementation.

Adult↗

PubMed1997

Yeast PIG genes: PIG1 encodes a putative type 1 phosphatase subunit that interacts with the yeast glycogen synthase Gsy2p.

The biosynthesis of glycogen involves multiple proteins that associate with each other and the glycogen macromolecule. In efforts to understand the nature of these proteins, a two-hybrid screen was undertaken to detect proteins able to interact with Gsy2p, a major form of glycogen synthase in Saccharomyces cerevisiae. Two positives expressed proteins derived from genes designated PIG1 and PIG2, on chromosomes XIIR and IXL respectively. PIG1 codes for a protein with 38% identity over a 230 residue segment to Gac1p, a protein thought to be a type 1 protein phosphatase targeting subunit whose loss impairs glycogen synthesis. Pig2p has 30% identify to the protein corresponding to an open reading frame, YER054, on chromosome V. Deletion of PIG1 on its own had little effect on glycogen storage but, in combination with loss of GAC1, caused a more severe glycogen-deficient phenotype than seen in gac1 mutants. This result is consistent with Pig1p being functionally related to Gac1p and we propose that Pig1p may be a type 1 phosphatase regulatory subunit. Delection of PIG2, YER054, or both genes together caused no detectable change in glycogen metabolism under the conditions tested. Gac1p, Pig1p, Pig2p and the YER054p are the only four proteins coded by the yeast genome that share a conserved segment of approximately 25 residues, designated the GVNK motif, that is identifiable also in RGI, the mammalian type 1 phosphatase targeting subunit.

Amino Acid Sequence↗

PubMed1997

Peptides and neuromas: calcitonin gene-related peptide, substance P, and mast cells in a mechanosensitive human sural neuroma.

We examined and compared a mechanosensitive human sural neuroma and a contralateral sural nerve collected simultaneously from a patient involved in a diabetic neuropathy research protocol. Using indirect immunofluorescence staining. we identified a striking difference in the content within axons of two neuropeptides, substance P (SP) and calcitonin, gene-related peptide (CGRP), between the contralateral nerve and the neuroma. Unlike the contralateral nerve, where immunofluorescence was sparse, a significant number of disorganized axon profiles that stained brightly positive for CGRP or SP were identified in the neuroma. In contrast, staining for tyrosine hydroxylase, a label of sympathetic axons, was largely absent except around one large arteriole. The neuroma specimen also contained large numbers of serotonin-containing mast cells, only noted occasionally in the contralateral nerve. The peptide staining and mast cell accumulation in the human neuroma closely resembled changes we have previously observed in an animal neuroma model. Local neuropeptides may play a role in the injury response of peripheral nerve, and may be related to mechanosensitivity.

Antibody Specificity↗

PubMed1997

Machado-Joseph disease: clinical, molecular, and metabolic characterization in Chinese kindreds.

Machado-Joseph disease, an autosomal dominant multisystem motor degeneration, has been described mainly in people of Portuguese descent. Our report documents the presence of Machado-Joseph disease in the Chinese population, based on the specific molecular marker of a CAG repeat array in the 3' end of the MJD gene. We screened 21 Chinese families with dominant spinocerebellar ataxia. The results showed that Machado-Joseph disease with CAG expansion accounted for 52% of families with autosomal dominant cerebellar ataxia in this series. The clinical characteristics, besides the well-documented cerebellar ataxia, dysarthria, nystagmus, corticospinal dysfunctions, a variable degree of facial muscle fasciculation, and proprioceptive loss, included loss of optokinetic nystagmus and autonomic nervous system dysfunction. The CAG repeat number in the MJD gene ranged from 14 to 39 among normal alleles, and from 63 to 81 among MJD alleles. There was a strong inverse correlation (gamma = -0.77) between number of CAG repeats and age at symptom onset, accounting for 60% of the variance of age at onset. A strong clinical anticipation of age at onset existed in successive generations. Mild instabilities of expanded CAG repeat numbers during meiotic transmission occurred, with no significant difference according to the gender of the transmitting parent. Finally, brain metabolism in Machado-Joseph disease, studied with positron emission tomography, was characterized by significant progressive regional hypometabolism in the occipital cortex, as well as the cerebellar hemispheres, vermis, and brainstem.

Adult↗

PubMed1997

Assessment of major life events for Hong Kong adolescents: the Chinese Adolescent Life Event Scale.

Previous Chinese research on adolescent life stress adopted life event scales that were directly translated from Western measures. To address the methodological and cultural issues overlooked by the "import" approach, the present research aimed at constructing a life event scale for Hong Kong adolescents. Study 1 was conducted to congregate items for the Chinese Adolescent Life Event Scale (CALES). The CALES contains 44 items derived from 618 Hong Kong adolescents. Study 2 revealed adequate test-retest reliability and criterion-related validity for the CALES. Moreover, the CALES yielded stronger relationships with depression than did the translated life event measures. Results suggest that the CALES is appropriate for assessing life events for Hong Kong adolescents. Both unique features of the CALES and life events found only in the translated measures are examined. Implications for Chinese research on life stress are discussed.

Adolescent↗

PubMed1997

A comparative study of the distribution of ofloxacin and ciprofloxacin in prostatic tissues after simultaneous oral ingestion.

OBJECTIVES: To determine the levels of two quinolones, ofloxacin and ciprofloxacin, potent broad-spectrum antibiotics with very good oral bioavailability and low minimum inhibitory concentrations (MICs) for most pathogens, in the prostates of patients who underwent transurethral resection of the prostate (TURP) after oral ingestion for surgical prophylaxis. PATIENTS AND METHODS: Twenty-eight patients with BPH requiring a TURP ingested 250 mg of both drugs 2-4 h before operation. The levels of the drugs in the serum and prostate were measured using high-performance liquid chromatography and the levels of both drugs determined at the 6 and 9 o'clock positions in the prostate to examine any local variations in drug concentration. RESULTS: Ofloxacin concentrations were significantly higher in the serum and prostatic tissues compared with ciprofloxacin for the same dose, but its penetrance into the prostate was lower. This mainly reflected its higher oral bioavailability. Both drugs were present in concentrations 50% higher at the 6 o'clock than at the 9 o'clock position but both exceeded the MICs for most Gram-negative organisms except Pseudomonas. CONCLUSION: Ofloxacin has the advantage against ciprofloxacin of exceeding the MICs for Staphylococcus and Chlamydia. However, ciprofloxacin has the advantage of having prostate-to-serum ratios of unity, but for the same dose the prostatic concentrations of ofloxacin is significantly higher.

Administration, Oral↗