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Biomedical subjects

S G Smith

Publications and source records attributed to S G Smith.

At least 37 records · Page 2Linked to original sources
PubMed1997

Control of Escherichia coli type 1 fimbrial gene expression in stationary phase: a negative role for RpoS.

Expression of type 1 fimbriae in Escherichia coli is subject to phase-dependent control, with many regulatory inputs from proteins which organise or rearrange the structure of DNA. Inversion of a DNA segment carrying the promoter for expression of fimA, the gene encoding the fimbrial subunit protein, makes a key contribution to the switching of cells between fimbriate and afimbriate states. We have discovered that transcription of fimA is repressed as cells enter stationary phase. This repression is not seen in isogenic strains deficient in rpoS, the gene coding for the stationary phase-specific sigma factor RpoS. RpoS-deficient strains are also altered in the frequency of inversion of the fimA promoter segment. In the strains used in this study, inversion is catalysed by an integrase-like site-specific recombinase encoded by the fimB gene. We report that fimB transcription is repressed strongly as wild-type cells enter stationary phase but that this repression is alleviated in cells deficient in RpoS. These data suggest that RpoS has a negative regulatory role which may be indirect, at both the fimA and the fimB promoters.

Bacterial Proteins↗
PubMed1997

Detection of low copy number inversions in mouse genomic DNA with unidirectional PCR primers.

The recessive brachypodism (bp) mutation, located in the growth/differentiation factor 5 (GDF5) gene, causes highly specific skeletal changes in the limbs of brachypod mice. Although Southern blot analysis does not distinguish sequence disruptions in the GDF5 sequence of brachypod mice, sequencing and mapping GDF5 mRNA reveals the bp mechanism to be an inversion preceded by a small deletion. We report here a simple and sensitive method of bp detection from mouse genomic DNA. Previous bp detection used degenerative PCR sequencing. However, without automation, sequencing is a laborious effort for GDF5 inversion detection. The method developed utilizes two unidirectional primers in PCR (UP-PCR), which allow for quick and sensitive analysis of gel electrophoresed PCR products. UP-PCR of the GDF5 gene in wildtype mouse genomic DNA cannot amplify a fragment due to the unidirectional primers. However, UP-PCR of the GDF5 gene in bp mouse genomic DNA does amplify a fragment from the GDF5 gene. Amplification occurs because of the inverted fragment in bp GDF5. This fragment changes the direction of the second forward primer 180 degrees to the position of a reverse primer. UP-PCR detection of the bp inverted fragment is highly sensitive. Amplified fragments were obtained from the bp genomic DNA in the presence of wildtype genomic DNA in ratios up to 1:10(6), respectively. The sensitivity and simplicity of this method allow for quick, inexpensive, and reliable detection of the bp inversion.

Animals↗
PubMed1996

Fimbrial adhesins: similarities and variations in structure and biogenesis.

Fimbriae are wiry (2 to 4 nm diam.) or rod-shaped (6 to 8 nm diam.), fibre-like structures on the surfaces of bacteria which mediate attachment to host cells. Much has been learned in recent years about the biogenesis, structure and regulation of expression of these adhesive organelles in Gram-negative bacteria. Analyses of the genetic determinants encoding the biogenesis of fimbriae has revealed that the adhesive interaction of fimbriae can be mediated by major subunits (CFA/I and CS1 fimbriae) or minor subunits (P, S, and type 1 fimbriae), with the adhesin being located either at the tip of the fimbria or along the length of the fimbrial shaft. Minor subunits can also act as adapters, anchors, initiators or elongators. Post-translational glycosylation of the type 4 pilins of Neisseria gonorrhoeae, Neisseria meningitidis and Pseudomonas aeruginosa has been demonstrated. The structures of the PapD chaperone of Escherichia coli and of N. gonorrhoeae type 4 fimbrin have been resolved at 2.0-2.6 A. Rod-shaped fimbriae should not be thought of as being rigid inflexible structures but rather as dynamic structures which can undergo transition from a helicoidal to a fibrillar conformation to provide a degree of elasticity and plasticity to the fimbriae so that they can resist shear forces, rather like a bungee cord. At least four mechanisms have been identified in the assembly of fimbriae from fimbrin subunits, namely the chaperone-usher pathway (e.g., P-fimbriae of uropathogenic E. coli), the general secretion assembly pathway (e.g., type 4 fimbriae or N-methylphenylalanine fimbriae of P. aeruginosa, the extracellular nucleation-precipitation pathway (e.g., curli of E. coli) and the CFA/I, CS1 and CS2 fimbrial pathway.

Adhesins, Bacterial↗
PubMed1996

Effects of distal femoral centralizers on bone-cement in total hip arthroplasty. An experimental analysis of cement-centralizer bonding, cement void formation, and crack propagation.

Distal femoral centralizers of five different designs were inserted into model femoral stems and cemented into closed-ended tubes simulating a proximal femoral canal. Specimens underwent cyclic loading from 50 to 500 lb. for 0, 1, 2, 5, and 10 million cycles. Each specimen was then sectioned transversely at multiple levels to obtain serial cross-sections, beginning at the femoral stem tip and proceeding distally so as to include the full extent of the centralizer. The area of each section occupied by a centralizer and the total amount of porosity present in the cement surrounding the centralizers were measured using an image analyzer. A dye penetrant was then applied to each section to visualize cement cracks and areas of incomplete bonding between cement and centralizers. The number, length, and location of cement cracks were catalogued for each section. No cement cracks or lack of bonding was observed at the interface between cement and centralizers. There was greater porosity in the specimens containing centralizers than in controls without centralizers (P < .05). The cement surrounding two of the centralizer designs had a significantly smaller amount of porosity than the cement surrounding the other three designs (P < .05). The number of cracks did not depend on whether a centralizer was used, the type of centralizer, or the cycling duration. In the control specimens, failure to adequately plug the centralizer receptacle hole in the stem tip resulted in very large cement voids.

Hip Prosthesis↗
PubMed1996

A gene for superoxide dismutase from Xanthomonas campestris pv. campestris and its expression during bacterial-plant interactions.

A recombinant plasmid selected from a library of Xanthomonas campestris pv. campestris genomic DNA by functional complementation of a superoxide dismutase (SOD)-deficient strain of Escherichia coli contained a gene encoding the major SOD activity of X. campestris pv. campestris. Inhibition and renaturation studies suggested that manganese was the metal cofactor for this SOD. Examination of the nucleotide sequence of an active subclone revealed a 612-bp open reading frame that encodes a protein with high amino acid sequence homology to a range of SOD enzymes. The sod gene was mutagenized with Tn5-lacZ. None of the insertions that abolished SOD-conferring activity were in the correct orientation for lacZ expression. Repeated attempts to introduce these insertions into the chromosome of X. campestris pv. campestris were unsuccessful and it was concluded that the sod gene may be essential for viability. In order to monitor the expression of the sod gene, a sod-gus transcriptional fusion was constructed. Expression of the sod gene varied according to the growth stage of the organism in culture. In planta, the sod gene was induced within 3 to 4 h of inoculation, with similar kinetics during compatible and incompatible interactions with turnip and pepper, respectively.

Amino Acid Sequence↗
PubMed1996

Neoral (cyclosporin) in dermatology: technical aspects.

Cyclosporin is a highly effective treatment for psoriasis, atopic dermatitis and many other inflammatory dermatoses. Absorption of cyclosporin from the traditional Sandimmun formulation is influenced by many factors, including bile flow, food and gastrointestinal motility. As a consequence, the bioavailability of Sandimmun is low and highly variable, both within and between patients. Neoral is a microemulsion preconcentrate formulation that has self-emulsifying properties and immediately forms a microemulsion in aqueous fluids, allowing rapid and consistent absorption of cyclosporin from the gastrointestinal tract. Benefits in dermatology are likely to be more patients responding at lower doses, a faster onset of action and a more predictable response to a given dose allowing for fewer dose adjustments. In the future these benefits of Neoral may lead to the simplified management of cyclosporin treatment and less frequent safety monitoring.

Chemistry, Pharmaceutical↗
PubMed1996

Detection of alcohol misusing patients in accident and emergency departments: the Paddington alcohol test (PAT)

OBJECTIVE: To develop an effective but practical screening questionnaire for use by accident and emergency (A&E) staff to detect alcohol misuse early on in its natural history, without unreasonably prolonging patient waiting times; and to integrate an alcohol health worker (AHW) into A&E to provide counselling for referred patients. METHODS: Two pilot studies for adult patients were undertaken to develop the 1 min Paddington alcohol test (PAT), which has only three compulsory questions for detecting alcohol misuse: two cover peak consumption and frequency of possible binge drinking, and the third asks whether in the patients' view their attendance at A&E was alcohol related. The use of the PAT was validated in "appropriate" adult patients over a one year period. Patients found to be positive were invited to attend the A&E review clinic for counselling by the AHW. RESULTS: The development of the PAT resulted in a referral rate of one patient per 158 A&E adult attenders, facilitating a counselling rate of one patient per 263 A&E adult attenders by the AHW. This counselling rate is a 10-fold increase on the rate of one patient per 2610 adult attenders found in a study undertaken during 1988-90. CONCLUSIONS: The use of the PAT is one practical method for A&E staff to detect the alcohol misusing patient for referral to a departmental alcohol health worker.

Adult↗
PubMed1995

One-year results of the intrascleral glaucoma implant.

This is an initial report from a study to determine the safety and efficacy of an implant placed within the sclera to relieve elevated intraocular pressure (IOP). It describes the first eight patients to receive the implant. Intraocular pressure and pneumotonometry were evaluated preoperatively and postoperatively for one year. In five patients, IOP decreased. Three patients in which the implant was considered a failure because of wound leaks had patch grafts, removal of the implant, or both. The five successful cases have continued to show reduced IOP.

Aqueous Humor↗
PubMed1995

Nodular prurigo responds to cyclosporin.

Nodular prurigo is a distressing disease which is difficult to treat. Two patients with severe nodular prurigo were treated with cyclosporin for periods of 36 and 24 weeks, respectively, using doses of 3-4.5 mg/kg per day. In both cases there was a reduction in the severity of pruritus after 2 weeks of treatment. In one patient there was a considerable, although incomplete response, and in the other almost complete resolution of the disease was achieved. The improvement was maintained throughout the treatment period, and the drug was generally well tolerated, although in one patient there was a rise in serum creatinine during treatment, which later returned to normal.

Adult↗
PubMed1995

Thoracic lymphatic cannulation for the study of pulmonary immune responses in lung lymph of calves.

OBJECTIVE: To develop a system for analysis of immune response variables in the lymph draining the lung and to establish baseline data for clinically normal calves. DESIGN: Surgery was performed on 6 calves to insert a cannula into the efferent lymphatic duct of the caudal mediastinal lymph node to create a long-term thoracic lymph fistula draining to the exterior. Lymph was collected daily, and on the fifth postoperative day, calves were exposed to an aerosol of cell culture medium (mock infection). For the next 10 days, lymph was collected for analysis and, on the tenth day, necropsy was performed. ANIMALS: Six 6- to 8-week-old Holstein bull calves. PROCEDURES: Daily lymph samples were evaluated for: flow rate; total and differential cell counts; and IgG, IgM, IgA, IgE, and protein concentrations. On days -4, -1, 1, 4, 7, and 10, cells were stained and quantitated by fluorescence-activated cell sorter analysis for T, B, CD4+, and CD8+ cells. Blood lymphocytes were evaluated on days -1 and 10 for comparison. RESULTS: Flow was established for up to 25 days, with a mean rate between 11 and 22 ml/h. Protein concentrations in lymph and plasma did not indicate a protein drain. Although mean lymphocyte counts reflected a slight gradual decrease in lymph lymphocytes, this effect was not apparent in every calf, nor was the effect seen in blood lymphocytes. There were no significant changes in IgG, IgM, IgA, or IgE concentration, with the exception of IgA concentration in 1 calf that developed an abscess at the cannulation site. The T-cell subset absolute numbers of CD4+ and CD8+ cells decreased slightly over time, but the CD4(+)-to-CD8+ cell ratio remained almost constant at near 2. CONCLUSIONS: Creation of a thoracic lymphatic fistula appears to be a useful technique for studying effects of lung infection on immunologic variables, with potential application to bacterial and viral respiratory tract diseases. CLINICAL RELEVANCE: Thoracic lymphatic cannulation can be used in studies to determine pathogenic mechanisms in respiratory tract disease and to develop more effective vaccines against respiratory tract pathogens.

Animals↗
PubMed1994

Effect of terbinafine on the pharmacokinetics of cyclosporin in humans.

Cyclosporin is largely metabolized by hepatic cytochrome P450 enzymes, and azole drugs that inhibit cytochrome P450 may precipitate cyclosporin toxicity. The allylamine terbinafine binds to a small subfraction of hepatic cytochrome P450 in type I fashion, and has no effect upon hepatic metabolism of cyclosporin in vitro. The purpose of this study was to determine whether oral terbinafine alters the pharmacokinetics of oral cyclosporin in vivo. Twenty male volunteers (age 19-44 years), were randomly allocated to two groups. The first group received three single oral doses of cyclosporin 300 mg at intervals of 21 d. The second and third doses of cyclosporin were preceded by a 6-d course of oral terbinafine 250 mg each morning. A further 250 mg of terbinafine was taken with the second and third doses of cyclosporin. Blood levels of cyclosporin and terbinafine were monitored for 36 h after each dose. The second group received a 7-d course of terbinafine 250 mg each morning. On the seventh day a single dose of cyclosporin 300 mg was taken together with the terbinafine. Blood levels of both cyclosporin and terbinafine were monitored for 36 h. Two further single doses of cyclosporin 300 mg were given at intervals of 2 weeks and the cyclosporin levels again monitored. In both groups each cyclosporin dose was preceded by an 8-h fast. The mean peak blood concentration of cyclosporin when taken alone was 958 micrograms/l, and 822 when taken with terbinafine. The mean area under the curve for cyclosporin was 4207 micrograms/l/h when taken alone and 3665 when taken with terbinafine. The mean absorption half-life for cyclosporin when taken alone was 0.29 h, and 0.33 when taken with terbinafine. The mean time of maximum concentration and elimination half-life of cyclosporin were unaltered by terbinafine. The results suggest that terbinafine is likely to prove a safe systemic anti-fungal treatment for patients who are taking cyclosporin.

Absorption↗
PubMed1993

Cytotoxicity of antifolate inhibitors of thymidylate and purine synthesis to WiDr colonic carcinoma cells.

We have studied the cytotoxicity of 5,10-dideazatetrahydrofolate (DDATHF) and of D-1694 to human WiDr colonic carcinoma cells as a model system for the effects of pure inhibitors of either the de novo purine synthesis pathway or thymidylate synthesis. The growth of this cell line was inhibited by very low concentrations of either agent and the lethality of DDATHF and D-1694 was completely prevented by continuous exposure to either hypoxanthine or thymidine, respectively, indicating that these compounds were very potent metabolic inhibitors, each specific for one of these pathways. D-1694 was highly cytotoxic (> 3 logs of kill) after a 4-h exposure to 1 microM drug, or a 24-h exposure to very low concentrations (0.04 microM). On the other hand, the cytotoxicity of DDATHF was substantially lower, with 2 logs of cell kill requiring >> 100 microM with 4 h of exposure or approximately 40 microM for 72 h of exposure. Maximal cell kill induced by D-1694 was 5-6 logs, consistent with elimination of all viable cells except preexisting mutants. A maximum of 2-3 logs of cell kill was observed with DDATHF. Exposure of WiDr cells to either D-1694 or DDATHF caused striking cellular changes, but the morphologies of cells treated with the two drugs were remarkably different. D-1694-treated cells detached from the dish within 1-2 days after a megaloblastosis, whereas DDATHF-treated cells remained adherent to the dishes for at least 10 days after treatment. The addition of thymidine to D-1694-treated cultures or hypoxanthine to DDATHF-treated cells after up to 20 h of drug exposure completely prevented cytotoxicity of either drug. With longer exposures, cytotoxicity of both drugs progressively increased in spite of such rescue. Our results indicate that substantial (99-99.9%) tumor cell kill can be induced by a pure inhibitor of purine synthesis, but that the rate of commitment to cell death and the extent of cell kill is greater with a pure inhibitor of thymidylate synthesis.

Acyltransferases↗
PubMed1993

Experimental studies to assess the potential of photodynamic therapy for the treatment of bronchial carcinomas.

BACKGROUND: Photodynamic therapy (PDT) is a technique for producing localised tissue necrosis with light after prior administration of a photosensitising drug. There is some selectivity of uptake of photosensitisers in malignant tissue, although this is difficult to exploit. Full thickness necrosis in normal and neoplastic colon heals without perforation because of a lack of effect on collagen, making local cure a possibility. The experiments described here aim to establish whether these conclusions are also valid for bronchial tumours. METHODS: In pharmacokinetic studies normal rats were given 5 mg/kg of the photosensitiser aluminium sulphonated phthalocyanine (A1SPc) intravenously and killed up to one month later. The distribution of A1SPc in the trachea was measured by chemical extraction and fluorescence microscopy. In subsequent experiments sensitised animals were treated with light delivered to the tracheal mucosa through a thin flexible fibre and the resultant lesions were studied for their size, mechanical strength, and healing. A series of resected human bronchial carcinomas were examined histologically for their collagen content. RESULTS: The tracheal concentration of A1SPc in normal rats was maximum 1-20 hours after administration. Fluorescence microscopy revealed that most was in the perichondrium and submucosal stroma, with little in the cartilage. Light exposure showed necrosis of the soft tissues which healed by regeneration, but no effect on cartilage and no reduction in the mechanical strength of the trachea at any stage. Histological examination of resected human bronchial carcinomas showed more collagen in the tumour areas than would be found in normal regions. CONCLUSIONS: PDT leads to necrosis of the soft tissues of the normal trachea but there is complete healing by regeneration, no risk of perforation (due to collagen preservation), and no effect on cartilage. Human bronchial carcinomas apparently contain more collagen than normal bronchi which may give protection against perforation following necrosis induced by PDT. PDT may have a role in eradicating small volumes of tumour tissue in situ and could be valuable for treating (1) small carcinomas in patients unfit for resection, (2) tumour remaining after surgical resection, (3) stump recurrences, or (4) to prolong palliation of tumours after debulking with the NdYAG laser.

Animals↗
PubMed1993

Listening and talking to patients. A remedy for malpractice suits?

This study evaluates the hypothesis that the way physicians communicate with patients and the degree patients perceive physician fault for bad medical outcomes are risk factors for the initiation of malpractice lawsuits. The study involved 160 adults who viewed a videotape of a physician treating a patient while using either positive or negative communication behaviors. Participants were told that the case had either a positive result, a bad result through no fault of the physician, a bad result for uncertain reasons, or a bad result that was the physician's fault. Participants then rated their litigious feelings. Results showed that the use of negative communication behaviors by the physician increased litigious intentions. An increased perception of physician fault for the bad result also increased litigious intentions. Uncertainty as to the reason for the bad outcome, however, raised litigious feelings nearly as much as did perceived physician fault. The results of the study support the hypothesis that altering the way physicians communicate and improving patient education can affect the risk of malpractice lawsuits.

Adult↗
PubMed1992

Surgical outcome of phacoemulsification combined with the Pearce trabeculectomy in patients with glaucoma.

The safety and efficacy of phacoemulsification and posterior chamber lens insertion combined with the Pearce trabeculectomy (PE/PCL/P-TRX) in patients with coexistent cataract and glaucoma was evaluated retrospectively. The Pearce trabeculectomy is a form of nonfiltration glaucoma surgery in which an inner block containing trabecular meshwork is excised under a scleral-pocket incision which is closed tightly. Thirty consecutive eyes sustained a reduction of mean intraocular pressure from 21.0 +/- 4.4 mm Hg to 16.6 +/- 3.3 mm Hg after PE/PCL/P-TRX at one year (P less than .001). The average number of glaucoma medications used was reduced from 1.9 to 0.8 postoperatively. At one year, 60% (18 of 30) of eyes treated with PE/PCL/P-TRX had intraocular pressures less than 21 mm Hg without medications.

Aged↗
PubMed1992

Keratoconus and bilateral lattice-granular corneal dystrophies.

The occurrence of lattice and granular corneal dystrophies in the same eye has been reported in individuals who trace their families to the province of Avellino in Italy. We present the first histopathologic report of keratoconus and bilateral lattice-granular corneal dystrophies occurring in the same patient. This individual's family also originated in Avellino, Italy.

Aged↗