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Biomedical subjects

A Steel

Publications and source records attributed to A Steel.

At least 19 recordsLinked to original sources
PubMed2006

NKG2C+ NK cells are enriched in AIDS patients with advanced-stage Kaposi's sarcoma.

Kaposi's sarcoma (KS) is an AIDS-defining condition in individuals with human immunodeficiency virus type 1 infection. We investigated the phenotype and function of the NKG2C+ NK cell population in individuals with AIDS and Kaposi's sarcoma. The staging of AIDS KS patients according to the AIDS Clinical Trial Group criteria revealed that patients with the S1 disease stage have a significantly higher proportion of NKG2C+ cells than those with the S0 disease stage. NKG2C+ cells from S1-stage patients are highly enriched for the expression of KIR3DL1, are depleted of NKp46, and respond poorly to major histocompatibility complex class I-positive target cells. These data demonstrate a link between NK cell phenotype and function and disease prognosis in AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed2004

Transmission of donor melanoma to multiple organ transplant recipients.

Malignant melanoma represents the most common tumour responsible for donor-derived post transplantation malignancies. We report the varied presentation and outcome of three graft recipients (two kidney and hepatic) who developed metastatic melanoma following cadaveric organ transplantation from a single multiorgan donor. Two of the recipients presented with symptomatic metastatic lesions and the third patient, despite being carefully monitored, developed evidence of metastatic cutaneous melanoma. Two of the patients died as a direct result of their melanomas. The recipients of corneal and cardiac grafts remain disease-free. We conclude that despite careful screening, donor-derived tumours remain a not uncommon clinical entity. The identification of a lesion in one recipient should prompt immediate examination and investigation of the remaining recipients of multiorgan donations.

Adult↗
PubMed2001

Evaluation of three-dimensional microchannel glass biochips for multiplexed nucleic acid fluorescence hybridization assays.

Three-dimensional, flow-through microchannel glass substrates have a potential for enhanced performance, including increased sensitivity and dynamic range, over traditional planar substrates used in medium-density microarray platforms. This paper presents a methodology for the implementation of multiplexed nucleic acid hybridization fluorescence assays on microchannel glass substrates. Fluorescence detection was achieved, in a first instance, using conventional low-magnification microscope objective lenses, as imaging optics whose depth-of-field characteristics match the thickness of the microchannel glass chip. The optical properties of microchannel glass were shown, through experimental results and simulations, to be compatible with the quantitative detection of heterogeneous hybridization events taking place along the microchannel sidewalls, with detection limits for oligonucleotide targets in the low-attomole range.

Base Sequence↗
PubMed2001

Young dyspeptic patients: with a test-and-treat policy, are the benefits of decreased symptom severity and oesophago-gastric-duodenoscopy workload sustained?

OBJECTIVES: To examine the symptom severity and requirement for oesophago-gastro-duodenoscopy (OGD) in young dyspeptic patients 2 years after serological testing for Helicobacter pylori, and to compare the outcomes of seronegative patients with those of seropositive patients. DESIGN: Long-term follow-up study of 232 participants from our previous trial. METHODS: Telephone assessment of patients' symptom severity, scored using a previously validated questionnaire; return of patients for OGD determined using local patient administration system (PAS); and review of medical case notes. RESULTS: Dyspepsia symptom severity of both seronegative and seropositive patients remained reduced compared with initial scores at time of trial recruitment. Symptom severity of seropositive patients was significantly lower than that of seronegative patients (P< 0.001). Seventeen additional patients returned for OGD between six months and two years after the start of the serological study. As 61 of the original 232 study patients returned for OGD within the first six month follow-up period, a total of 78 individuals (34%) had OGD during the two years following the study. Thus, 66% of the original participants avoided OGD. CONCLUSIONS: This study of non-invasive testing for H. pylori in young dyspeptic patients has demonstrated an improvement in symptom severity and a substantial reduction in OGD workload over a 2-year period.

Adult↗
PubMed2000

Functional roles of histidine and tyrosine residues in the H(+)-peptide transporter PepT1.

Histidyl residues in peptide transporters PepT1 and PepT2 are believed to participate in proton and substrate binding and to be crucial to the transporters' functional activities. In the present study, we performed mutagenesis of rabbit PepT1. We mutated three histidine residues (H57, H111, and H121) predicted to reside in transmembrane segments, as well as tyrosine residues adjacent to H57. Functional analysis of wild-type and mutant PepT1 expressed in Xenopus oocytes, using both the radiotracer methods and two-microelectrode voltage-clamping, revealed that not only the H57 but also the aromatic residues near H57 were essential for the normal function of PepT1, in agreement with the concept that aromatic residues stabilize the charge on H(+) when interacting with H57. While mutagenesis at H111 did not significantly affect the activity of PepT1, mutagenesis at H121 had profound implications. The substrate affinities for H121 mutants were decreased depending both on the charge of the substrate and the charge on the substituted residues at position 121. We propose that H57 and H121 are intimately involved in the binding of the coupling ion H(+) and the recognition of transportable peptide substrates, respectively.

Amino Acid Substitution↗
PubMed2000

Differential recognition of ACE inhibitors in Xenopus laevis oocytes expressing rat PEPT1 and PEPT2.

PURPOSE: To examine the mechanism of inhibition of glycylsarcosine (GlySar) transport by quinapril and enalapril, and whether or not angiotensin converting enzyme (ACE) inhibitors are transported by PEPT2 as well as by PEPT1. METHODS: Xenopus laevis oocytes were cRNA-injected with rat PEPT1 or PEPT2 and the transport kinetics of radiolabeled GlySar were studied in the absence and presence of quinapril and enalapril. The two-microelectrode voltage-clamp technique was also performed to probe the electrogenic uptake of captopril, quinapril and enalapril. RESULTS: Kinetic analyses demonstrated that quinapril inhibited the uptake of GlySar in a noncompetitive manner in Xenopus oocytes injected with PEPT1 or PEPT2 (Ki = 0.8 or 0.4 mM, respectively). In contrast, a competitive interaction was observed between GlySar and enalapril (Ki = 10.8 mM for PEPT1 or 4.3 mM for PEPT2). Most significantly, captopril and enalapril, but not quinapril, induced inwardly-directed currents in both PEPT1- and PEPT2-expressed oocytes. CONCLUSIONS: These results are unique in providing direct evidence for the substrate recognition and transport of some ACE inhibitors by the high- and low-affinity oligopeptide transporters. Our findings point to differences between PEPT1 and PEPT2 in their affinity to, rather than in their specificity for, ACE inhibitors.

Algorithms↗
PubMed2000

Day-case percutaneous endoscopic gastrostomy: a viable proposition?

The aim of our study was to evaluate the success rate, complications, and long term outcomes following day-case percutaneous endoscopic gastrostomy (PEG). This retrospective study was carried out in a 650-bed District General hospital in Northamptonshire, UK. Thirty-six patients, aged 28-90 years, were included in the study, 21 males (58%) and 15 females (42%). Indications for PEG insertion included head and neck cancer, dysphagia as a result of primary disease, and AIDS-related malnutrition. Data were collected from the medical and dietetic records. The PEG procedure was successful in 33 patients (92%). In 32 cases (97%) the patient was discharged home. Twenty five of the patients (76%) suffered no complications whilst seven (21%) suffered complications within a month of the procedure. No patient required further surgical intervention. Five patients (15%) died of their primary disease within a month of the procedure. Patients had had their PEG tubes in situ for up to 2.5 years at the end of data collection. We conclude that PEG can be performed as a day-case procedure in stable patients with no increase in complication rate, morbidity, or mortality.

Adult↗
PubMed1999

Reducing the endoscopic workload: does serological testing for Helicobacter pylori help?

OBJECTIVE: Serological screening for Helicobacter pylori (H. pylori) in young (< or = 45 years) dyspeptic patients has been used to avoid oesophago-gastro-duodenoscopy (OGD). We used serology to identify seronegative and seropositive patients without sinister symptoms and combined approaches of avoiding OGD in both groups. We aimed to determine the reduction of OGD in this group. DESIGN: Prospective study on the treatment of 232 patients with dyspepsia. SETTING: Six hundred and fifty bed district general hospital serving rural Northamptonshire, UK. INTERVENTIONS: Two hundred and thirty-two patients referred by local general practitioners for OGD were offered serology. Symptom severity was scored using a questionnaire. One hundred and eleven seronegative patients received symptomatic treatment, 105 seropositive patients received triple therapy for 1 week. Sixteen patients with equivocal results were offered OGD. Patients were followed up after 6 months. MAIN OUTCOME MEASURES: Severity of dyspepsia symptoms and proportion of patients returning for OGD. RESULTS: Fifteen equivocal patients underwent OGD, one refused. Forty-six patients (33 seronegative, 13 seropositive) had persisting symptoms and underwent OGD. Mean symptom severity was reduced significantly in equivocal (P<0.01), seronegative (P<0.001) and seropositive (P<0.001) patients. Fewer seronegative patients were symptom-free at follow up compared to seropositive patients (n = 15 (16%) vs n = 48 (51%); P<0.001), 171 patients avoided OGD, a 74% reduction. CONCLUSIONS: Use of H. pylori serology in the management of young dyspeptic patients without sinister symptoms can reduce the OGD workload by 74%, decreasing the length of time that older patients, who are at greater risk of malignant disease, may have to wait for OGD.

Adolescent↗
PubMed1998

hPepT1-mediated epithelial transport of bacteria-derived chemotactic peptides enhances neutrophil-epithelial interactions.

Intestinal epithelial cells express hPepT1, an apical transporter responsible for the uptake of a broad array of small peptides. As these could conceivably include n-formyl peptides, we examined whether hPepT1 could transport the model n-formylated peptide fMLP and, if so, whether such cellular uptake of fMLP influenced neutrophil-epithelial interactions. fMLP uptake into oocytes was enhanced by hPepT1 expression. In addition, fMLP competitively inhibited uptake of a known hPepT1 substrate (glycylsarcosine) in hPepT1 expressing oocytes. hPepT1 peptide uptake was further examined in a polarized human intestinal epithelial cell line (Caco2-BBE) known to express this transporter. Epithelial monolayers internalized apical fMLP in a fashion that was competitively inhibited by other hPepT1 recognized solutes, but not by related solutes that were not transported by hPepT1. Fluorescence analyses of intracellular pH revealed that fMLP uptake was accompanied by cytosolic acidification, consistent with the known function of hPepT1 as a peptide H+ cotransporter. Lumenal fMLP resulted in directed movement of neutrophils across epithelial monolayers. Solutes that inhibit hPepT1-mediated fMLP transport decreased neutrophil transmigration by approximately 50%. Conversely, conditions that enhanced the rate of hPepT1-mediated fMLP uptake (cytosolic acidification) enhanced neutrophil-transepithelial migration by approximately 70%. We conclude that hPepT1 transports fMLP and uptake of these peptide influences neutrophil-epithelial interactions. These data (a) emphasize the importance of hPepT1 in mediating intestinal inflammation, (b) raise the possibility that modulating hPepT1 activity could influence states of intestinal inflammation, and (c) provide the first evidence of a link between active transepithelial transport and neutrophil-epithelial interactions.

Animals↗
PubMed1997

Symmetry of H+ binding to the intra- and extracellular side of the H+-coupled oligopeptide cotransporter PepT1.

Ion-coupled solute transporters exhibit pre-steady-tate currents that resemble those of voltage-dependent ion channels. These currents were assumed to be mostly due to binding and dissociation of the coupling ion near the extracellular transporter surface. Little attention was given to analogous events that may occur at the intracellular surface. To address this issue, we performed voltage clamp studies of Xenopus oocytes expressing the intestinal H+-coupled peptide cotransporter PepT1 and recorded the dependence of transient charge movements in the absence of peptide substrate on changing intra- (pHi) and extracellular pH (pHo). Rapid steps in membrane potential induced transient charge movements that showed a marked dependence on pHi and pHo. At a pHo of 7.0 and a holding potential (Vh) of -50 mV, the charge movements were mostly inwardly directed, whereas reduction of pHo to below 7.0 resulted in outwardly directed charge movements. When pHi was reduced, inwardly directed charge movements were observed. The data on the voltage dependence of the transient charge movements were fitted by the Boltzmann equation, yielding an apparent valence of 0.65 +/- 0.03 (n = 7). The midpoint voltage (V0.5) of the charge distribution shifted linearly as a function of pHi and pHo. Our results indicate that, as a first approximation, the magnitude and polarity of the transient charge movements depend upon the prevailing H+ electrochemical gradient. We propose that PepT1 has a single proton binding site that is symmetrically accessible from both sides of the membrane and that decreasing the H+ chemical potential (DeltamuH) or increasing the membrane potential (Vm) shifts this binding site from an outwardly to an inwardly facing occluded state. This concept constitutes an important extension of previous kinetic models of ion-coupled solute transporters by including a more detailed description of intracellular events.

Animals↗
PubMed1997

Stoichiometry and pH dependence of the rabbit proton-dependent oligopeptide transporter PepT1.

1. The intestinal H(+)-coupled peptide transporter PepT1, displays a broad substrate specificity and accepts most charged and neutral di- and tripeptides. To study the proton-to-peptide stoichiometry and the dependence of the kinetic parameters on extracellular pH (pHo), rabbit PepT1 was expressed in Xenopus laevis oocytes and used for uptake studies of radiolabelled neutral and charged dipeptides, voltage-clamp analysis and intracellular pH measurements. 2. PepT1 did not display the substrate-gated anion conductances that have been found to be characteristic of members of the Na(+)- and H(+)-coupled high-affinity glutamate transporter family. In conjunction with previous data on the ion dependence of PepT1, it can therefore be concluded that peptide-evoked charge fluxes of PepT1 are entirely due to H+ movement. 3. Neutral, acidic and basic dipeptides induced intracellular acidification. The rate of acidification, the initial rates of the uptake of radiolabelled peptides and the associated charge fluxes gave proton-substrate coupling ratios of 1:1, 2:1 and 1:1 for neutral, acidic and basic dipeptides, respectively. 4. Maximal transport of the neutral and charged dipeptides Gly-Leu, Gly-Glu, Gly-Lys and Ala-Lys occurred at pHo 5.5, 5.2, 6.2 and 5.8, respectively. The Imax values were relatively pHo independent but the apparent affinity (Km(app) values for these peptides were shown to be highly pHo dependent. 5. Our data show that at physiological pH (pHo 5.5-6.0) PepT1 prefers neutral and acidic peptides. The shift in transport maximum for the acidic peptide Gly-Glu to a lower pH value suggests that acidic dipeptides are transported in the protonated form. The shift in the transport maxima of the basic dipeptides to higher pH values may involve titration of a side-chain on the transporter molecule (e.g. protonation of a histidine group). These considerations have led us to propose a model for coupled transport of neutral, acidic and basic dipeptides.

Animals↗
PubMed1996

Molecular cloning and characterization of the vasopressin-regulated urea transporter of rat kidney collecting ducts.

Absorption of urea in the renal inner medullary collecting duct (IMCD) contributes to hypertonicity in the medullary interstitium which, in turn, provides the osmotic driving force for water reabsorption. This mechanism is regulated by vasopressin via a cAMP-dependent pathway and activation of a specialized urea transporter located in the apical membrane. We report here the cloning of a novel urea transporter, designated UT1, from the rat inner medulla which is functionally and structurally distinct from the previously reported kidney urea transporter UT2. UT1 expressed in Xenopus oocytes mediated passive transport of urea that was inhibited by phloretin and urea analogs but, in contrast to UT2, was strongly stimulated by cAMP agonists. Sequence comparison revealed that the coding region of UT1 cDNA contains the entire 397 amino acid residue coding region of UT2 and an additional 1,596 basepair-stretch at the 5' end. This stretch encodes a novel 532 amino acid residue NH2-terminal domain that has 67% sequence identity with UT2. Thus, UT1 consists of two internally homologous portions that have most likely arisen by gene duplication. Studies of the rat genomic DNA further indicated that UT1 and UT2 are derived from a single gene by alternative splicing. Based on Northern analysis and in situ hybridization, UT1 is expressed exclusively in the IMCD, particularly in its terminal portion. Taken together, our data show that UT1 corresponds to the previously characterized vasopressin-regulated urea transporter in the apical membrane of the terminal IMCD which plays a critical role in renal water conservation.

Amino Acid Sequence↗